Celtic Heroes

Defensive ability quests are obtained at "Ancient Statues" throughout the zones. These are not class specific. There are three in Lir's, one in Crookback, and one in Shalemont. For each of these quests you will have to collect some objects (gems, clovers, crowns, leaves, or stones).

Clovers you can pick up off the ground in the pasture by the Tavern.
Crowns are found by knocking over three other statues (Northern Pen in Lir's, Behind the Tower on Mage Hill in Shale, and at the 1st island in Stone).
Gems are a bit annoying as you will probably have to slaughter in Crookback and DC to get them (you need 5 different gems) or buy them from another player.
Leaves are dropped from four Dryads (the walking trees) in Lir's.
Stones are dropped by certain mobs in Shale.

Statue locations:

Lir's - Near the waterfall next to the Tavern.
Lir's - Near the waterfall by the Castle/Jill the Cow Herder.
Lir's - Beside the windmill behind Highshore village.
Crookback - In Redstone Cavern.
Shalemont - Up the hill at Greygorge, around the corner from the missing party.

These abilities will start to level once you complete the quest. If you are level 55, for example, you will start at 0/550. These abilities allow you the chance to shrug off enemy skills. So if a Connacht Mage casts a Fireball at you, you might withstand it. Melee attacks are not affected by these skills, however, so a Bloodgove hitting you with a staff will still have a high chance of hitting/interrupting you.

The 5 Skill/Spell Blockers

Warding: Offensive Magic Deflection. Skills such as Lightning Bolt, Storm's Touch, Firebolt and Iceshards.

Fortitude: Offensive Skill Deflection. Skills like Pummel, Mighty Blow, Sneaky.

Vigour: . Offensive DoT & Debuff dodging. Skills like Rend, Vines, Barbed Shot, Howling Wind?

Willpower:. Skills like Freeze and Shield Bash, lures

Reflex:. Skills like Bolas, Roots