Unless you're talking about a pull where mobs come from different locations, it is trivial to hold aggro against trash mobs as a tank versus the healer. Healers usually get aggro because someone broke CC on a mob that the tank wasn't doing any aggro on (because it's CCed).
The problem with aggro is usually you've some DPS who take aggro without claiming responsibility. That is, any competent DPS should be able to solo even the killer dogs in Mandolorian Raiders by using stuns and, if needed, defensive CDs. But they don't do this. Honestly when you get jumped by 5 dogs you really would prefer the tank get 3 while each DPS picks up 1. You don't have to heal the DPS because they can each solo their dog (would come pretty close to dying, but they should win), so this leaves you with only 3 dogs to worry about on the tank which is certainly better than 5 dogs. Most likely you see a DPS get aggro and then they put the deaggro so that killer dog goes back to the tank, and while you're healing the DPS (who no longer has aggro) the tank dies. If you simply ignore the DPS dying everything should work out okay unless that DPS can't solo a strong by himself (in that case you're likely to have other problems later).
Simple solution, triage. The DPS is not worth heals on that pull, unless you're throwing an instant AoE bomb heal the tank and have your own aggro wipe ready to go if necessary. You know the damage on that pull is obscene, the tank _must_ live a DPS can die.