Keeping hate on multiple targets

[Enfarious]

If telling them to follow marks isn't working. You can always let them tank, don't try to save them from their folly, and in some instances, for the really thick headed ones, tell your healers to let them die. Sometimes it's only a few deaths that gets the point across to let the tank tank.

Edit: Of course, in pure trash mob sections sometimes it's not even worth trying since things will die faster than issues arise, or DDs will be doing more damage than you can even hope to overcome.