[drktmplr12]

If the has a weapon that procs, you are usually pretty safe casting it after it does.

Distance also plays a role. The farther you are when you cast spells, the less likely a mob is going to beeline to you because of a slow.

Another alternative if you don't have a heavy caster group is to root the mob and have the tank use proximity agro. This is assuming the melee in your group understand that a rooted mob hits the closest thing to it.