I say if your willing to do the work you can teach the dog. Keeping them away won't change the behavior. Exposure and correction with redirection while on leash. Also a lot of times I find dogs to be fence fighters but when the fence is not between them, no more problem.
Terriers are a challenge.
The easiest thing, instead of just telling the dog what they can't do,... show them what they can. An acceptable alternative. When I am at the tractor with my queensland heeler he will bring me a frisbee which I happily throw. When I see his eyes start to focus, I stop it immediately. My lab mix has a hard time not jumping on us and nibbling fingers when excited. we taught her to get a toy which keeps her mouth occupied and keeps her from jumping. This one hunts everything that moves in our backyard often successfully! I can see the temptation in her eyes sometimes. And my labra- bull has food aggression so we don't give out treats next to her.
For us, there is no hope of unsupervised free ranging when chicks are too little and squeaky. But all are free ranging by around 8 weeks.
For some reason people with little dogs often don't teach any discipline. Like it's no big deal they scratch up your calf, pull at the end of the leash, pee in the house, start stuff with big dogs,.... (not finger pointing). But ALL dogs can be trained if you take the time and see what really makes them tick. That being said, each dog is an individual. If after you spend your time training they still let you know that their desire outweighs the training then it's best to heed their body language and don't put them in a situation where you may not like the outcome. With a dog that age, I would think if you had a strong relationship with them that they would want to do what please you.
If you try the whole exposure thing, make sure the dog is well exercised first and they should be more cooperative. And praise or reward behaviors that are desirable. For us a firm NO is good with the alternative and praise offered. They get an occasional smack on the muzzle if it's warranted, nothing abusive. I'd be more likely to grab the neck, force the dog to the ground in a submissive position until calm while being semi-surrounded. Once calm, release. Of course you have to be calm as well.
Sounds like your dog wants to "play" with them and is excited.
Hope this helps at all. I love my dogs and my chickens and have spent tons of time teaching appropriate behaviors (they aren't perfect). It can be done though. I have lots more advice for integration, but you are the key.
But some animals just aren't fit to certain situations. I used to love going to the dog park. But my fixed female LOVES to steal the fun and toys from other dogs. I had to accept that I couldn't take her anymore. Same dog hates wheels of all kinds... strollers, skateboards, bicycles, etc. Now I can't even take her to Home Depot (one of my favorite places for outings when it's raining)! That is just something I will not be able to change and have to accept. I'm sure you will figure out what is the right choice for you.
Best wishes!
