I am repeating myself here, but Sue said something that is very critical, to my mind, in training dogs to stay away from your birds. FEAR. HEr dog FEARS the geese. And there in lies your potential hope. IT is not a quick cure and you have to put aside a few days of time to accomplish it. But with the dog being young, you have a chance.
What is he scared of? Popping ballons? Air horns? FIrecrackers? What startles him and makes him jump? I've used empty pop cans with a few pennies or pebbles inside, the cans tied to strings. ARmed with my pop cans and the new dog I head down to the chicken pen. I SAY NOTHING to the dog. I DO NOTHING to indicate how he should or should not act towards the chickens. (the chickens are locked up at this point, obviously) I take a seat somewhere near the pen, but not hovering over the dog. I wait for the dog to approach the fence, rigid with excitement at the potential chase, tail wagging eagerly as he thinks about what he is going to chew on and then.....BLAM! I slam a few cans down beside him as hard as I can!
BUT...I say nothing, I do nothing, in fact I try to not even look at the dog. Because he needs to learn that it is not ME who is doing this, but the invisible chicken god in the sky who is always watching and will always blam some scary noise at him when he looks at the chickens. Without comment and without going over to the dog, I slowly reel the cans back to me by the attached strings. This is all about the element of surprise. Scary, jarring, unpleasant surprise.
Repeat this performance. If the dog quits being startled by your object, quit and find another object. If the dog leaves the chicken fence and comes to you for comfort, pat him on the head, tell him he is a good boy, but do not go overboard on the squeaky, enthusiastic praise. Give him praise, but if he wanders away from you and back to the chicken fence, time for next round of "Don't Tempt THe Chicken God!"
WHen you do scare him, do not say anything. Just act as if it had nothing to do with you. In fact, look skyward and mutter, uh oh, someone has made him mad today! YOur dog needs to get the idea that interst in chickens is rewarded by the unpleasant sensation of sudden fear. He needs to learn that lesson in a BIG WAY. SO if you have to blow up a bunch of balloon and pop them one at a time with a pin, or have an air horn in your pocket (wear ear plugs) or hurl cans without looking like you are...then that is what you do. But find what startles him and use it to your advantage. Negative association = chickens are scary. STAY AWAY FROM THEM!
I do not tie dead chickens to my dogs. I do not beat them with dead chickens. I have had dogs that are bear chasers, are SPCA rejects and have all manner of mental issues. But I have NEVER lost a single bird to one of my dogs. Never. And this 'Chicken God' method is the one I use in every case. IT has worked waith mature SPCA dogs as well. Find what scares them and then scare them...while pretending its' not you doing it.