I never had aggro issues single box tanking on my prot warrior. Just charge in, thunder clap, take a step back, and shockwave stun em all. Then it's just basically devastate and cleave until tc and sw are off cd. If you can't charge the caster type or if there is more than one of them use heroic throw on them to pull them to you to make sure they get your aoe too.
I actually thought holding aggro was easier as warrior when not boxing but it does take more concentration which makes it harder while boxing.
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