SoManyHats, I'm sorry about your dog killing your hen. As some on here might know, I'm very passionate about dogs. So I'm posting my opinion here. It isn't directed at you. It's just some info about dogs and my opinion.
Dogs are predators. Some more than others. I know that all 5 of my dogs would kill a chicken. I try very hard to never give them a chance. That's my responsibility. I can try to train my dogs to leave the chickens alone. Some dogs can be trained, some can't. That doesn't make it a bad dog. All my dogs are hunting dogs, even if that's not in their breed standard (I have 2 Bostons -non sporting group). All my dogs have high prey drive. I don't mind that, but it makes it doubly important to keep my birds away from my dogs, and I brood in the house. Accidents happen. The best you can do is take responsibility and learn from those mistakes. Don't blame the dog. He's doing what nature tells him to do. There's a popular saying in dog agility that drives me absolutely crazy. I hate this saying, but it's "train, don't complain". I'd rather it be train your dog, but remember, they are a dog.