Also, with dogs, some breeds will be easier to use as guards than others, though any dog can probably be discouraged from killing chickens. Some will be easier to break from this than others. Maybe you could get some bigger birds like turkeys or something if you don't want a dog. Roosters are good guards as well, like others have said, but if it's a roo you really like, just know that he'll protect the hens, but depending on the threat, you may have to be prepared to look for a new rooster afterward.
Back to dogs, I've heard many people say they have Great Pyrenees for the purpose of guarding their other animals, so if you change your mind about a dog, maybe that's something to look into. I've been thinking of looking into them myself since so many people seem to use them as predator deterrents.