I also had a stray kill some of my chickens and my favorite two ducks once too. It was a very sweet dog but I bet it was just hungry. It was a lab mix. Some breeds may be more prone to attacking chickens then others but it varies by dog. I knew a chihuahua that was the quietest, friendliest dog ever, all the time. While most are nuts. I've also had a number of Collies over my life time and they are generally a very laid back, friendly dog but I had a male that bit me when I first got him because he was trying to keep me away from his food (we worked through that issue and he had no problem with it at all after a few months). I know some terriers that are true terrors and some that are wonderful. One seems possessed and will never stop barking and growling at you even though I was with her almost every day for hours because her owner was my best friend's mom and I know another that is the sweetest thing on earth and doesn't have a mean bone in her body and only barks when she's crated and wants to be out. So my advice pick a size, pick a breed that usually has a good temperament that comes in that size, and then look at dogs that match that description. Good luck.