Nope, not possible. You can't get enough def to avoid being hit all together, you can't get to 100% block with items, same goes for dodge and parry.
But you, as a paladin, have Holy Shield which increases block chance and should be kept up all the time.
Def cap is 540 and that's enough so that bosses can't crit and that's all you need because normal attacks which don't crit can be controlled by armor, block and parry or even defensives. Going above that cap does benefit you, but it's not necessary even though you will pass the cap from gear alone.
So what was uncrushable in TBC is uncrittable in wotlk, same effect, different way of getting there.