I guess I'm no dog lover, and although I don't suppose I would have shot them right away, I'd try my best to hunt down the owners, inform them of the situation, and make it clear that you'll exercise your right to shoot them if they come back.
Consider, for example, what might happen if you're not there, and the dogs attack your kid's bunny cage, and the kid (assuming small kid who loves his/her bunnies) attempts to intervene. So what if "dogs kill rabbits?" Dogs that kill rabbits should be out in the country somewhere, killing their own damn rabbits.
As I said, I guess i'm not much of a dog lover, but I think people who choose not to have dogs should not have to defend themselves or their own animals against other people's dogs, nor should they have to step in other people's dogs**t in their own yards. Millions and zillions of people know how to handle their dogs and train them and keep them where they belong. Those who don't get little sympathy from me.