I am having a bit of problem getting adequate threat on the 1st and 2nd phases with the three separated bosses. We have been marking them... they are separated by enough space that TC and SW dont quite get them all. Usually trying SS/Dev TC SW and then charge to third one that hasnt been hit. By the time I hit the second one the ranged spell caster or projectile shooter has mauled my party. I have good gear and spec (I think) as I have been using tankspot for improvement. Any advice would be helpful. The World of Warcraft Armory
Try to get the group to kill them all in one spot, that's the biggest thing you can do to get snap agro on all of them. Once they stand up, don't do anything yet. They seem to reset agro once they start running around. Just wait for them to start moving, and then do a challenging shout. Throw out a thunderclap and then a shockwave. They should stick to you pretty well after that. Some groups zone out after dismounting and then run back in, you can do that if you feel cowardly :P
I am pretty sure that the threat everyone built up on them while mounted sticks with them even when the ground phase begins. Therefore, you will have to taunt each one of them (real taunt, not aoe taunt) in order to get them on you. I usually aoe taunt 2 of them off the bat and charge the 3rd and taunt it. I then have a few sec to taunt the other 2.
You can have your entire group run out after the Champions are dismounted and save yourself the hassle. When your group walks back in all three will be standing by the gate waiting patiently for you.
I find it helpful to cast Heroic throw at the caster in the group to silence them right off the bat, then charge one of the others and let off a thunderclap for snap aggro. If there's only one caster, I'll just charge the hunter if he's there, or just the next closest one if he isn't. If there's two casters, I'll heroic throw to silence one, then charge the other and shield bash immediately, THEN let off thunder clap. While they're silenced they'll try to stay in melee range instead of hanging back to cast. That gives you enough time to get em in a nice group and let off a thunder clap and shockwave before you start your normal threat rotation.
This is probably stupid to mention, but make sure your dps is waiting til you've picked them up to let loose. I've dropped probably 4 pugs this week because they've started attacking the boss before I've even had a chance to smack the bad guys. This instance isn't hard but it does take a little more coordination than most other heroics. If your group can't get its act together don't feel obligated to try and pull them through it, there's probably dozens of other groups forming that need a tank anyway!