The one thing I hate about bark collars altogether is they taught my dog Autumn to growl when she greets people. This could eventually lead to a bad situation if somebody assumes she is aggressive (which she is not). I got her when I still lived with my parents and my stepdad insisted on a bark collar. She learned quickly that it won't pick up a low growl and so she was conditioned that a bark is not ok but a growl is. Even though its been years without the collar, she still has more tendency to growl instead of bark. What have you tried to redirect their attention? Will a bone get their full attention? Can you try a blind of some sort over their runs?

Whatever you choose, try to find a bark collar that takes normal batteries if you decide to get one. What a pain trying to find specific batteries!