The Protector is a very defensive class. Not only does it get access to high defense equipment and naturally have very high VIT, but many of its skills reduce damage taken in some manner.

However, damage in EO2 works quite differently than it did in EO1: your defense *divides* the damage you take rather than subtracts from it. So instead of seeing situations where 60% reduction reduces a 200 damage attack to 1-5 damage in EO1, you'd get 80 damage instead in EO2. 60% reduction *means* 60% reduction.

Of course, that's where some of the other skills come into play.

Oh, and from now on, I'll be referring to "Blunt" element as Crush now -- Blunt was making little sense when it was applying to things like Feast, Smite, Axes, and the like.

Shields
Max Level: 10. No Requirements.
Your basic Mastery skill. Unlike EO1, however, Shields now reduces all damage taken, no matter the element.
L1 Stats: 99% Dmg Taken
L5 Stats: 95% Dmg Taken
L10 Stats: 90% Dmg Taken

Aegis
Max Level: 10. Reqs: L5 Holy Aura, L5 Last Stand.
If your Protector dies, Aegis gives you a chance of reviving. However, even if it works, it can only do so once per battle. (Or rather, I've yet to figure out if anything other than a new battle resets your Aegis skill)
L1 Stats: 20% chance of reviving
L5 Stats: 24% chance of reviving
L10 Stats: 29% chance of reviving

En Garde
Max Level: 10. Reqs: L5 Shields.
A simple chance per attack to halve the damage you take. Works on area attacks and enemy skills too. The chance doesn't improve a lot with levels, but at least 1 point in here is a good start.
L1 Stats: 20% chance to halve damage
L5 Stats: 24% chance to halve damage
L10 Stats: 29% chance to halve damage

Holy Aura
Max Level: 5. Reqs: L1 HP Boost.
This low level passive skill simply restores a small amount of HP to the Protector at the end of every turn. While not a significant amount, it can add up over long battles, and meshes well with the Protector's overall durability. But points are probably better spent elsewhere.
L1 Stats: Heal 3 HP per turn
L5 Stats: Heal 7 HP per turn

Last Stand
Max Level: 5. Reqs: L3 HP Boost.
This nice skill reduces all damage you take, and gets better the lower your HP. There are 5 HP Brackets: 100%-76% (no change to base), 75%-51% (-4% Dmg), 50%-26% (-10% Dmg), 25%-11% (-14% Dmg) and 10%-0% (-20% Dmg). Higher levels in this skill increases the base reduction of damage by 2% per level. Note that the skill is a little [BUGGED]: the 76%-100% bracket for L1 should have been 100% - instead, it's 97%. This is the only skill level and only bracket where this is bugged: at L2, the same bracket *increases* to 98%, and then proceeds normally. Not a big bug though, since you'll likely be maxing this skill anyways.
L1 Stats: 97%/96%/90%/86%/80% Dmg Taken
L5 Stats: 92%/88%/82%/78%/72% Dmg Taken

Smite
Max Level: 5. Reqs: L10 Shields.
A powerful Crush attack with a chance of inflicting Arm Bind. Highly accurate, too. Since it's the only damage skill the Protector gets, it's probably something you'll end up getting. However, given the TP cost's steep rise and the more gradual rise in stats per skill level, you may want to hold off on maxing it until later. LUC increases the chance to bind.
L1 Stats: 10 TP, 300% Dmg, 20% Spd, 200% Acc, 20% chance of Arm Bind
L5 Stats: 18 TP, 400% Dmg, 120% Spd, 200% Acc, 30% chance of Arm Bind 

F.Guard/B.Guard
Max Level: 10. Reqs: L1 Shields.
The first Guard abilities you get access to: these allow your Protector to help reduce the damage other party members take. When you activate a Guard ability, the Protector uses it at the very start of the turn, and it stays active until the end of the turn or the Protector dies. Each Guard ability starts with a 100% chance of activating during the turn, and this reduces at a particular rate every time the ability is successfully activated. When it does succesfully activate, the Guard's effects are then applied, helping reduce damage in whatever way the skill allows.

F.Guard and B.Guard protect the Front and Back Rows respectively. At max skill levels, they reduce damage by a good amount and don't fail very often. Also note that these skills only work against attacks that use the physical elements - attacks that use none of the physical elements are unaffected.
L1 Stats: 2 TP, Reduces damage by 15%, 100% base chance to guard, -100% chance per hit
L5 Stats: 6 TP, Reduces damage by 25%, 100% base chance to guard, -64% chance per hit
L10 Stats: 11 TP, Reduces damage by 60%, 100% base chance to guard, -10% chance per hit

Full Guard
Max Level: 5. Reqs: L5 F.Guard, L5 B.Guard.
Full Guard combines the effects of F.Guard and B.Guard. However, the damage reduction is a bit less and the chance reduction per hit is rather high: there is no way you can use this to protect an entire 5-character party from an area attack.
L1 Stats: 6 TP, Reduces damage by 13%, 100% base chance to guard, -100% chance per hit
L5 Stats: 14 TP, Reduces damage by 49%, 100% base chance to guard, -32% chance per hit

Choice Guard
Max Level: 5. Reqs: L7 Shields.
This skill allows you to restrict your defense to a single ally. It's more effective than the other physical Guard skills, and protecting only one character means that the chance reduction won't matter so much. However, it's not that much more effective than F.Guard or B.Guard, especially if you're not expecting a huge number of attacks. A single point could be useful at times, but whether you max it or not will depend on your strategy.
L1 Stats: 2 TP, Reduces damage by 35%, 100% base chance to guard, -50% chance per hit
L5 Stats: 10 TP, Reduces damage by 65%, 100% base chance to guard, -10% chance per hit 

Antifire/Anticold/Antivolt
Max Level: 10. Reqs: L3 Shields.
These Guard abilities work on the Fire, Ice and Volt elements alone. But, like all Guard abilities, their chance of success decreases during the turn as they successfully reduce or nullify damage. This can be critical for elemental areas: even L9 still has a 10% reduction in success rate per hit, giving a 70% chance that the ability will fail for at least one person if you're protecting a 5-character party from an area. The amount of damage taken depends on the skill level: total immunity is only available by L8, and L9 and 10 offer increasing amounts of absorb. As such, you can only really count on these abilities once they're at L10. You'll be happy to note, however, that any statuses an elemental skill will inflict are also annulled by any Absorb, not just Immunity -- a pleasant change from EO1.
L1 Stats: 2 TP, 50% Dmg Taken, 100% base chance to guard, -90% chance per hit
L5 Stats: 6 TP, 24% Dmg Taken, 100% base chance to guard, -50% chance per hit
L10 Stats: 11 TP, 50% Dmg Absorbed, 100% base chance to guard, -0% chance per hit

Tri Guard
Max Level: 5. Reqs: L10 TEC Boost, L10 Shields.
A combination of all three Anti-elemental skills. Since it grants absorption when maxed, it's a powerful skill. However, be warned: the success reduction per hit is quite high, and *cannot* protect the entire party from even a single area attack. That said, multiple Protectors working in tandem might do better... but multiple Protectors working in tandem could just use seperate Antis.
L1 Stats: 6 TP, 50% Dmg Taken, 100% base chance to guard, -100% chance per hit
L5 Stats: 14 TP, 10% Dmg Absorbed, 100% base chance to guard, -28% chance per hit

Fortify
Max Level: 5. Reqs: L1 VIT Boost.
The standard 5-turn defensive buff we're familiar with. It only works for the physical elements mind, and only for the Protector. Still, low cost in both Skill Points and TP and a quite reasonable reduction to go with it.
L1 Stats: 3 TP, 200% Spd, 90% Dmg Taken
L5 Stats: 7 TP, 300% Spd, 64% Dmg Taken

Provoke
Max Level: 10. No Requirements.
Another 5-turn defensive buff! But this time, with an additional provoke effect. The Provoke chance is the chance per enemy that, at the start of the turn, they will pick the Protector as the target of their attack. Since they pick their target at the start of each turn, casting Provoke during the turn (even via 1st Turn) won't affect their decision. Also, some enemies are immune to Provoke, and it obviously won't have any effect on skills that aren't single target. The Provoke effect maxes at L7: further skill levels increases speed and reduces TP and damage taken.
L1 Stats: 3 TP, 100% Spd, 20% Provoke, 100% Dmg Taken
L5 Stats: 7 TP, 130% Spd, 70% Provoke, 88% Dmg Taken
L10 Stats: 6 TP, 235% Spd, 100% Provoke, 73% Dmg Taken

Parry
Max Level: 5. Reqs: L3 Provoke.
Like the Guards, except that it only works for physical-element melee attacks, and only for the Protector using the skill. However, it does completely annul the damage taken. Maxing the skill isn't too great an idea though, since it only increases the chance of successive guards throughout the same turn, and it's rare that the Protector will be hit enough times during that. Still, it all depends on your formation and strategy - if you know your Protector is going to be targetted a lot and the enemy uses melee attacks a great deal, then this skill can be very useful.
L1 Stats: 3 TP, 100% base chance to parry, -40% chance per hit
L5 Stats: 7 TP, 100% base chance to parry, -5% chance per hit 

Refresh
Max Level: 5. Reqs: L1 TEC Boost.
Basic single target Refresh spell. The statuses it heals maxes at L4 - the only difference between that and L5 is the decrease in TP Cost from 4 to 1. Note that all versions of Refresh except the Medic's single target version can *not* heal Petrify.
L1 Stats: 1 TP, 50% Spd, Removes Blind
L5 Stats: 1 TP, 100% Spd, Removes Blind/Poison/Sleep/Paralyze/Terror/Curse/Confuse

Flee
Max Level: 5. No Requirements.
This skill allows you to escape the current battle, providing it can be escaped in the first place. On top of that, if you entered the current floor from another floor, you have a chance to be teleported to that previous floor, right in front of the staircase you used to enter the next one. Flee will activate at the start of the turn, before any enemy gets to move. Levels in this skill only increase the chance to warp and decrease the TP cost. Finally, note that on the first turn of a Pre-emptive battle, the chance to warp will always be 100%. Whether this is a beneficial effect or not will depend on your situation and playing style.
L1 Stats: 5 TP, 60% chance of warp
L5 Stats: 1 TP, 100% chance of warp

Mine
Max Level: 5. No Requirements.
Won't be covering it here.

FORCE SKILL: Perfect Defense
The perfect defense indeed: for a single turn, the entire party will take 0 damage from everything and be immune to all status attacks. Using this at the right time can be extremely useful indeed.
Stats: Immune to all damage and statuses for current turn 

Oh, and since I forgot to mention: Fortify and Provoke both only reduce damage against the physical elements. Your only real defenses against non-physical stuff are Shields, En Garde, Last Stand and the Antis/Tri Guard skills.