Since you have no socket bonus to worry about in an Eternal Belt Buckle, you should generally just use whatever your primary stat is (in the case of a tank, Stamina). You shouldn't be at zero avoidance though :S
You don't have 0 avoidance. Pretty much, avoidance is the combination of dodge and parry ('cause they completely remove a damage in the table.)
The 102% (actually, 102.4%, if you want to be precise) is the Uncrushable count (although there are no more crushing blows in Raid bosses now.) Basically, this is the sum of Dodge, Parry and Block. If this reaches 102.4%, it means that no direct hit from bosses will hit you: You'll either dodge, parry or block it (although blocking won't remove too much damage.)
Right now, I'd gem it with pure stam. But, with the announced changes in 3.2.2 for Touched by the Light, I'd try one of the new epic gems with str+stam.