Another thing that will work is human pee around a perimeter. Most of the time. Keep your birds penned, covered sides and top as well, unless you can be outside with them. I deal with these everyday and agree with SpeckledHen. Coyote mothers are raising and teaching their young right now. It will only get worse unless you do something now. You've been given the right and best answers to your problem. If you don't act and provide a place for your roosters to go or are actively with your birds when they are outside, you will lose them. Coyotes will take out cats, small dogs, whatever they can. They have even attacked children. Unless your dog is a trained guard dog, the results are going to be hit or miss as you've sadly found out. I don't mean to seem harsh, but if you don't stop with the utopia idea of keeping chickens, you'll be crying a lot more than you are now. Wild animals do not care what you think or want. All they care about is the survival of themselves and their young. You want to have an "Eat at Joes" sign outside your coop, have at it. They have already learned they are welcome there and will return. How you handle it from here is the only way to stop it. Call the Game Warden if you can't do it yourself. That's what they are there for.
I am very sorry this happened to your bird. It was an awful experience for him, as well as for you. Please, listen to the advice given and act accordingly.
I am very sorry this happened to your bird. It was an awful experience for him, as well as for you. Please, listen to the advice given and act accordingly.