Quote Originally Posted by Roffel View Post
If that tank is to dumb to notice a sleep that was casted then he shouldn't be tanking
Isn't that a bit extreme?! it's pretty easy to miss it if you're not expecting it. Also, it's not just for the Tank, everybody contributing to DPS should be informed so they don't AoE or dot other mobs (assuming the group actually want to CC the fight).

But to the OP, a good tank would notice you casting sleep and start proactively marking the one HE wants to be slept (again, if that's what the group wants to do).