My cats have never gone after even the tiniest of my bantams, although they've had "fun" with all of my chickens, by hiding and jumping out to startle them
Actually, taking your dog on a leash around your birds is a good idea. That by itself won't train him, but it's a step. Since your dog is well trained, I'll presume he knows the "leave it" command??? If not, then start teaching him now, with treats and such...then transfer that to your birds. Teaching your dog that the chickens are part of YOUR pack is important. These are not just any birds, they're your pack birds.
My retrievers were very easy to train around my birds, and my sister-in-law's hyper little jack russell learned quickly too (so that now when she comes to visit, her dog can run around the yard with no chicken issues other than poo eating).
I started by sitting in the run with my birds and dogs (I trained individually of course), requiring my dog to sit or lay down, my hand on the collar. Use whatever command you want to use - "leave it" or "gentle" or whatever, just always use the same command.
After a week or two (I trusted my male quicker than my female) of daily training, I moved on to the same thing, but just with the dog(s) on a short leash - still sat out in the run with everyone. Still required dogs to sit/down. After another week or two of daily training...
We moved on to me walking around beside my dog in the run, without the leash. You get the picture...
Then we moved on to walking around outside the run, with the birds free ranging.
Lastly, I'd have the dogs/chickens out, would act as if I was going about my business while scoping out the dog/chicken situation... Always use your command words if things look iffy.
My dogs will chase black birds and hawks from the nearby fields when they're swooping low or land nearby, but are wonderful with my chickens...
Train daily and consistantly...praise and correct.
