Sounds like you are doing a great job with him. And I think you've already got some great training advice. I just wanted to share my experience with our dog.
When we first got our chickens, I set up a crate in the garage next to the brooder box. I put my pointer, Puck, (a 3 year old bird-crazed hunter) in it whenever we were there doing something with the chicks and then I would leave him there for 1/2 hour at a time. I made a point of holding the chicks near him. The command "leave it" was invaluable and once he was able to remain calm when they were held near him, he was allowed to sniff them. My real aim was to desensitize him enough that he did not rush or lunge at the fence once the chickens were outside in the yard.
When we moved the chickens to the coop, we tied him out next to for short periods. Soon we found that when he was loose in the yard, he would often lie in front of the chickenyard gate and the chickens would flock to him and talk to him. When visiting dogs come near their yard, they all run into the coop. When a neighbour's poodle recently ran onto our property and rushed up to the fence, Puck, who is normally VERY friendly with other dogs, was fiercely barking, growling and chasing the dog away from the coop. When the chickens have gotten out of their yard (before we put netting over top), he didn't respond at all, he just lay there and occasionally sniffed a passing bird. And yet he will still chase wild birds that he sees at the feeder and will hunt gamebirds.
Our new puppy is growing up with the chickens, and is learning a lot about being a chicken guard dog from Puck.