as i've told many chicken keepers, NEVER GET DOGS AS GUARD ANIMALS!! they will kill your flock when you're not looking. no matter the breed, no matter the size, no matter the training. they all have the predatory urge to kill small animals, including chickens. for protection, use geese or emus. they are certainly less expensive to hatch from eggs than dogs, and if you let a broody hen raise them, they will grow up bonded to that flock, willing to risk their lives to protect it. a stinking mutt will only pretend to love the flock in return for treats and food, and will kill your chickens without hesitation once it stops receiving treats. geese and emus are the way to go. many online hatchereys carry goslings, and you can find emu eggs usually under 60 us dollars on eBay.
I disagree we had a female pitbull that was an excellent farm dog. We got her when she was two, and we had horses. She was good with them. When she was about 8 we added chickens, sheep and pigs to our farm. She would go in the pasture and never bother any of them. She slept in the orchard with the chickens, they would crawl on her even eat her food. She never killed or chased a single chicken. I think some how she could tell the difference between the animals that were suppose to be part of the farm and wild animals, because she would chase and kill rabbits and rats. We even trained her to watch for hawks, eagles and herons (we have a koi pond). If she saw them circling the pasture or pond she would run the fence line barking at the birds in the sky until they flew off. We had chicks in the house in a tote and she would look in the tote and watch them. Sadly she passed away at age 14 and a half. We would like to get another dog, but not sure we can find a replacement.