Your dog just has a high prey drive. It doesn't mean that he will harm anybody. I have a husky who has a high prey drive also. So far he has killed a skunk, two ducks, numerous bunnies, birds and mice. The one that was the hardest to take was the little stray kitty that came in our yard. I don't think there's anything you can do to prevent it. Just keep an eye on him at night. I wouldn't want Harley to get hurt.