Lead is your solution. High velocity lead! Once a predator gets a taste of blood and knows where the meal ticket is, good luck keeping it out, especially if the owner of the dog doesn't discipline. Now, there are less lethal lessons you can use. Rock Salt in a .410 Shotgun. That works for dang near everything. I know my advice is not PC or kind, but neither will the dog if he gets ahold of a chicken. Animals think in terms of "Is the risk worth the reward?". If the consequences are quite painful, the one may outway another. But understand this, if he gets one, he will more than likely never be broke of the habit. Other than that, keep em under lock and key or behind some friendly electric fence. And don't spare on the Joule rating. Seen dogs bolt under .5 joules before. 1 joule will light up a dog enough that it will be his last go round.