There are many training methods available but it will depend on your ability as a trainer which one you use. There is Cesar's method if you are the 'Pack Leader' type, which it doesn't sound like you are. There are shock collars available if you are not bothered by the idea of the shock collar. I use a spray bottle with water for my Pittie who hates water, but that is only effective as long as I am between him and the chickens.
The bottom line is dogs will be dogs and chasing chickens is just pure fun for them. We have 7 dogs of various sizes in our family and have surrendered the idea of training them to leave the chickens alone, so we have designated a yard for the chickens and a yard for the dogs, never the twain shall mingle.
Of course there's always a tractor so the chickens can free range a different area of the yard each day, but that is work for you to move the tractor each day. Good Luck with whatever you choose.