We had the same problem with my Son's Pomeranian/Dashund mix, Bradley. He absolutely LOVES chasing my Girls, they hate it. We installed a zip line for the dog. Now he can run around, but the Chickens are smart enough to avoid his territory. In fact, shortly after it was put up and the dog was attached, two of my hens walked up to the point where they were just out of reach and gave poor Bradley a MAJOR talking to. It was quite funny, watching their indignant attitude during the rant, and their satisfied air went they stomped away to go about thier business.