Just trap the bastards then finish them off come dawn.
I didn't bother to read BC's regs, but around here they are no different than gophers - you can shoot them year round with no need for a tag. I think you're supposed to have a conservation license.
I hate to agree with Tungsten, but a donkey will also work. Ornery bastards those things.
Llamas work too, but the root of the problem is that the pack is established and won't leave.
The best (most effective) way to remedy the problem is to kill the pack and then keepp a few llamas or donkeys in with the horses, as well as a few large herding dogs, like maremmas