The backyard is enclosed in 5' chainlink fencing with a tension wire along the bottom so the dogs can't squeeze underneath.More than likely you will get a couple in the yard every now and again. My chickens will forget about the dogs and fly in every so often and it usually ends in a bad way. In my experience if you have one dog that kills they will teach the other one how to also. Best of luck. Do you have netwire or chain link fence? As long as they can't fit through a hole in the fence into the yard I find it doesn't happen as often.