Radical thought...remove the off-tank?

[aesteval]

Nope. The whole reason the 2 tank and 2 healer party comp exist is because if one falls you always have a backup. It allows the party to recover. Think about how much more frustrating content would be if because the tank died you had to wipe and start over because you have no one to pickup the slack from their death.

That assumes that the offtank takes over though. *thinks about the time in a trial where half the party died before the offtank had aggro and even then it appears to have been unintentional to actually get aggro*

Fortunately, that's not a common scenario.