Tanks can't keep aggro.

[Jpec07]

Better Tanks than me have given me some sound advice. "If they want to keep taking the hate from you let them keep it."

As a career tank, I will say: that's bad advice. If a DPS is just being a fool and attacking the wrong target after you've marked, that's one thing, but if a healer pulls off you? You'd better make damn sure you get that enmity back, or else your ass is going to die. The worst thing you can do as a tank is piss off your healer - you are nothing without them.

Really, as a healer, the only thing you can do is make sure they're in their tank stance, and make sure not to pre-HoT them, and to attack the right target. Otherwise, enmity really isn't too much your responsibility, and hate loss is on the tank.