Pala tank, its a mix of defence, sta, dodge, block etc. And ofc spelldamage for threat. Dont go wild on the spelldamage, get the def cap first (isnt that hard to do actually) then go for avoidance so you hit the uncrushable mark, after that gather some more spell dmg.

mainTankadin, great site to get more info on what to gear for, and how to gear.
http://www.failsafedesign.com/maintankadin/index.php