How do you scare a 300-pound black bear? For the last four years, national park biologists have been evaluating various aversion methods to keep bears at a safe distance from humans. They’ve shot bears with rubber slugs, used slingshots and pepper spray, thrown rocks, even chased them on foot. Overall, aversive conditioning reduced but did not eliminate incidents of bears entering developed areas to forage for food. Shooting bears with rubber slugs from a 12-gauge shotgun was found to be slightly more effective than any other method.