I would suggest using a Warlock or Hunter's pet to do your tanking.

I am currently using Priest/Mage/Warlock and I find that my VW does a pretty good job of tanking. My biggest problem is agro management. If my VW can't keep agro it's a pretty quick wipe...

I have done fairly well in instances with this combination, but for some bosses like Archaedas in Uldaman you really need an off-tank.