I wouldn't get rid of the dog just yet. Sounds like it can be trained. Let the chickens out to free range while dog is on the leash.
Each time the dog seems like it's staring at a chicken, redirect by yanking on the chain and say "NO" in a low, mean voice.
Keep doing that, and the dog will look elsewhere.
Next, sit or stand with your leashed dog and throw out some scratch, calling the chickens over. Let the chickens get close. Each time the dog even "looks" at the chickens, yank the leash and say "NO". Make sure the dog sits quietly with the chickens right there.
Always praise him for looking the other way. Give him a little milk bone after he tolerates the chickens eating nearby if he doesn't lunge at them.
After the dog gets used to that, let him off the leash while the chickens free range. Keep his attention giving him a milk bone every few minutes. Walk around the yard with the bones so he'll follow you.
If he does run after the chickens, get him, grab his snout with one hand, push him onto his side with the other. Make him stay on his side on the ground keeping his head pressed hard against the ground....saying NO the entire 30 seconds. That's how dominate dogs teach the young ones.
This will take many days, maybe weeks.
Depending on the dog, it may NEVER work.
ALWAYS supervise your dog until you feel completely comfortable.
I have raised 3 Golden Retrievers with my method and they protect and love the chickens, never harming them.
Keep up posted on your progress or decision.