Afaik, crushing blows only occur, on mobs of much higher lvl than you (3+) - ie a bosslvl mob who is considered 3 lvls above you, can crush. Source: http://maintankadin.failsafedesign.c...opic.php?t=331

So to tank fairly well in heroics, uncrittable will do fine. 485 defense will make you uncrittable against lvl 71-72 mobs. 490, and you're "safe" from boss'es also (real raidbosses, not heroic ones)

Next is adding avoidance so you don't get hit that often, or at least mitigate the dmg somewhat. And here, defenserating, dodgerating, parryrating and blockrating/value comes in handy.

Each point of defense, increases your chance to dodge, parry and block by a mob. It also decreases the chance a mob will hit/crit you. The critchance for mobs are all 5% for equal level. 5.6% for bossmobs.

Resilience is a cheap way to reduce the chance to be critted, so for a tankadin, the S2 gavel (mace with spelldmg) is a really good starterweapon for tanking, along with stuff that has stamina, dodge, defense, block and parry.

Dodge, Parry and misschance are all complete avoidance. These will make you take less frequent hits from meleemobs. Block is partial avoidance, and can be compared somewhat to armormitigation. It reduces the dmg you take. In case of bossmobs, it also prevents crushing blows and/or crits. (by the time you reach uncrushable, you are allready crit-immune)

The more total avoidance you have, the better. But do not forget stamina! Stamina lets you survive streaks of hits, that would otherwise kill you. (sounds simple, I know) So yes, definately gem for stamina, at least in the beginning. Imo.

Regarding spelldmg, it is the bread and butter for your tanking. Seal of Righteousness and Seal of Vengeance scale very will with +dmg, so does consecration and holy frisbee. Judging SoV and SoR scales poorly, but it still adds a nice threatboost if you need it. Once you get a bunch of "pala plate" with both stamina, avoidance, sockets and spelldmg on it, you will never go back.

Str adds very little threat, low amount of dps (your abilities don't rely on +str/ap) and a pathetic amount of blockvalue. It's below +spirit in usefulness for tanking. (yes, I truly mean that)

Agility adds a bit of dodge - but is also a low priority, considering the amounts needed to get decent dodge. If a shaman is in your group, you will almost always want Wrath of Air over Grace of Air, and Stoneskin over Strength of Earth. And mana totem ofc

Lots of more reading about tanking as a paladin, head on over to http://maintankadin.failsafedesign.com - they have a very large source of information about everything a tankadin needs to know.