Cardboard assassin tinker
Figured I'd let everyone know that hasn't experienced the joy that is cardboard assassin... it could quite possibly be the most overpowered enchant in the game at the moment for avoiding damage.
It works on all tauntable bosses and will often times eat 2-3 swings from the boss before it dies. I'm sure someday soon it will get nerfed... but in the meantime all engineers (tanking or not) should have this enchant on their belt and use it proactively. The amount of damage your tank can avoid because of it HUGELY outweighs the amount of damage plasma shield will negate.