Stone Guards were pretty easy. We got Jade, Cobalt and Amethyst.
The way we did it was:
Warrior (me) started tanking amethyst. DK tanked cobalt +jade. Now, 2 different scenarios could occur.
1. Cobalt or jade debuff = keep tanking like you already are
2. Amethyst debuff = taunt jade or cobalt, when the with debuff reaches ~50 energy, the DK taunts the one giving the debuff. Resulting in debuffing one overloading.
From here it's very simple. If one of the mobs who're already together starts applying his debuff, keep tanking them as you are. If the lonely one starts giving the debuff, taunt the one who just overloaded and has no energy. Rinse and repeat until dead.
We did this with a warrior + dk tank and druid + shaman healer.