This might sound a bit elaborate, but I would be pissed enough to try something a little elaborate to keep more of my calves from dying. You could set up a make-shift and hopefully coyote proof run, and put your noisiest calf in there over night. Just make sure that its away from the herd so that the calf starts calling for mommy. I would think that coyotes would come running to that, and when they do you know what to do next. You might even want to bring a friend or three with you to help with the shooting, so you can kill as many as possible before they high tail it out of there!