I just got such a kick out of your videos! I've never seen a chicken and dog carry on like that! I think that as long as you continue with what you are doing-- taking him with you when you go to the chickens, keeping a really close eye on him and correcting him if he gets too carried away he will be fine in time.
I have 2 dogs--a blue heeler and a blue heeler/black lab mix. When they were puppies they would chase the chickens all the time when I would go out to tend the chickens. I would tell them "no" if they started to chase them and praise them when they listened. I would give them a treat and praise when they came to me and left the chickens alone.
And, yes, sadly they did kill a few. It was my fault as I left them unsupervised and they got carried away with their play.
In time they learned to leave them alone. Now they look out after them.
The other day while I was looking out the window I saw 2 of my roosters starting to fight. Their hackles were up and they started to jump at each other. My blue heeler was standing right next to them. All of a sudden she grabbed one by the head and pulled it away! I thought oh boy that was going to be the end of that rooster! Well, she just let it go!! And then she herded the 2 of them back to the chicken coop. I couldn't believe she knew to break up a rooster fight. I really wonder what was going through her mind? She is 2 yrs old now and has calmed down and learned alot. She is very smart. I think she learned a lot of chicken lessons on her own that I wasn't able to teach her!