I think it's still a good idea to work with your german shepherd. Even if you don't count on him to be protection, he needs to be trained to leave chickens alone.
And it sounds like he enjoys playing with toys, soft ones especially. Get him some new soft balls, or anything like stuffed toys but NOT anything that looks like animals. I am not an experienced trainer but the way I trained my dog was to "correct him" anytime he looked at or showed interest in the chicks. I used the tssst! sound and finger poke in the neck - quick like a bite - whenever he stuck his nose in or when he got that "too interested" look in his eye. Your dog is young and sounds like he needs to be exercised before chicken time and to get it out of his head that chickens are play toys. Whatever else you do, keep working with your gs and maybe he will be trustworthy someday soon. You could even hide out and watch him to correct him as soon as he starts paying attention to the birds. I don't even let my dog get started if you know what i mean.
