Jan 31st 2009 5:48PM For the Horseman fight, we've found the best way to tank the back bosses was to use an affliction or demo specced warlock (with doomguard) to tank one, and a shaman or paladin to tank the other. The warlock simply lets the doomguard attack the boss, throws up a DoT or 2 (more if he has points in the imp. DS talent), and then cast health funnel and drain life. If done properly, the warlock should take virtually no damage and and paladin can focus exclusively on his boss. At 3 stacks of the debuff, switch, rinse and repeat.
We've used this strategy successfully 9 times now (5 heroic, 4 normal), and every time we've downed the bosses on the first time (the one exception being the first time, where we wiped because of communication/confusion errors, not because of strategy flaws).