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Until you have the gear for it, no way.

Make your spec, but keep getting gear at least until your defense is at 540. While you are trying to get gear, stoneskin will help a ton in getting your def rating up. I don't know much about dual wield except my initial knowledge of it which was "STAY AWAY" and I know it's getting better for dps, but idk about tanking. I've always use 2h weapons.

TLDR version: Until your gear/gems/enchants get you at 540 def, don't even think about it. Nothing worse than a non def-capped tank.

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Well, I disagree VERY SLIGHTLY with Abhorred.
For heroics (where the bosses are generally level 80, not 83) the def cap is 536. Also, the def cap is totally 100% mandatory in raids, since a crit from a boss is basically a wipe. Heroics. . . .meh.

Tanks of any class need to balance out a few things; threat generation, avoidance and health.

These days most tanks just pile on the +stam. Since many of the stam numbers can get you to 40k health in T8 level gear, that's what's popular now. Still . . . I'd rather lose 1k health (from 40k to 39k) for 1% avoidance. There is a lot of math involved, and there is no clear answer to which is better.

Nevertheless, skill > gear. But with tanking, skill is not enough. Having about 28k health unbuffed, D at least 536 and about 50% avoidance for a DK should be enough for every heroic (perhaps not ToC). I encourage you to find a healer willing to train you (hopefully somebody with an alt that tanks) and do UK and Nexus on heroic. They are easy. You can almost certainly survive with a good healer, regardless of your gear, and it will teach you to use your cooldowns, your rotation etc.

I love tanking, it is so much more involved than dps-ing. It really makes WoW seem like a different game!