I know next to nothing about coping w/bears. it sounds like you're in a tough spot. I was thinking that since they are animals very dependent on their sense of smell, to set up a hot pepper bomb close to, or attached to the coop. rig it up in such a way that they trigger the pepper bomb all over themselves & up their sensitive noses. or, make a noise bomb that is very obnoxious to them. make it an unpleasant experience for them that outweighs the possibilities of fresh meat. that's a big order & if their food is in short supply - it won't work; however, if they have ample food & are just taking advantage of an opportunity - that might turn them away.