Prot Warrior, Threat,Def

[Almatomador]

this is my armory link
The World of Warcraft Armory (http://www.wowarmory.com/character-sheet.xml?r=Draka&n=Almatomador)

My question is i have been putting def, and dodge+stam gems in my gear, and was wondering, should i just go ahead and raise my def over 540? should i put some expertise gems or enchants on my gear? im finding that i hold aggro very well even with 3-5 group mobs, but it doesnt take long for me to lose aggro.

also as a tank i have seen alot of different people stacking stam or dodge or hit and exp. rating, wat should i do, should i stack stam gems or stay the way it is ? thank you for all your help guys

[Paramount]

There's absolutely nothing wrong with having more than 540 defense.

That being said, the way you gear really depends on your situation.

If you are having trouble surviving, then you should gem more towards stamina.

If your healers say you are hard to heal you should gear more towards avoidance (defense or dodge gemming here).

If you have dps riding on your coat tails threat wise, gem for expertise.
Since you say that you're having trouble with threat, then you should probably drop the dodge/stam gems in favor of exp/stam gems.