I wouldn't count on the dogs keeping the chickens in. I have visions of the dogs charging the fence, the chickens getting startled and popping over and you finding a mess. And, something I've noticed with my own chickens and dogs, eventually they get used to the dogs being there. And at some...
Just something that pops out from your original post: Your 4ft tall fence. Training may keep the dogs out, but your fence might not be able to keep your chickens in (depending on breeds). A 4ft fence easily contains my Silkies and frizzles, but my normal feathered breeds can fly over 6ft tall...