I've been running dungeons lately on tank jobs, and I notice a recurring problem. DDs who just attack whatever, regardless of marks, rather than focusing on a single target. Oftentimes both DDs are attacking their own target, meaning I cannot simply switch to their target.

What should I do in this situation? Spam flash and basically do no damage? Run back and forth between both of them and pray half my enmity generation is sufficient to keep hate? Or just keep being an ornery bastard who declares if they want to tank so bad, then let them?