Ive heard but not tried but some say to tie the dead bird around the neck of the dog and let it rot and it will make them have a complex about them afterwards lol. Try at your own risk.He had a problem last year when he was still an adolescent. I had to train/punish him and I think it worked... so far this year he has been perfect.
All my previous German Shepherds had the same problem. But I was able to get the number down to one chick a month.