I would talk with him again and let him know that the chickens are eating your corn. Keeping a civil relationship with him is most important since the problems could get much worse than losing a little bit of corn. The responsibility is on him to keep his stock on his own property and he should be aware of that. I had a similar problem a couple of years ago with some neighboring dogs and after repeated problems with them getting on to my property I had a lawyer draft a letter telling him that he was in violation of town leash laws and that the dogs weren't welcome on my property. A copy was sent to the town and suddenly he had a contractor there and spent thousands fencing in his whole yard. The law was on my side and if he had co-operated he wouldn't have had to spend the bucks to guarantee that the dogs stay on his place. Chickens in the freezer would be a last resort but it sounds like the guy is a moron who would just keep buying them.