I'm not sure this is the best place to put this but I have some questions regarding training/teaching dogs. I have two dogs. One is a 4.5-5 year old female (mama) and the other is a 3 year old female (daughter of the first). They are a mix breed. Lots of blue heeler, corgi, australian cattle dog type looks and personality. The litter we chose the daughter from appears to have been sired by a lab breed. They are undeniably the best childrens dogs I have ever seen or met. My kids have climbed on them, layed on them, ridden them (before getting caught and disciplined), etc. These dogs have never shown any aggression towards the children, they have never nipped, and only once can I recall even the slightest growl of dislike. They are very submissive dogs: they love their bellies rubbed and will plop down for that treatment readily. They are not spayed. When we got chickens this spring, aggression reared it's ugly head towards the birds. Collectively they have only killed one chicken, but countless times have gone after them. What can I do to teach them that the chickens are off limit? Or is it not reasonable to think this behaviour can be broken? I feel it can but what are the opinions of others and suggestions?