Of Wolves and Men: An Idea

I just read an article about the controversy surrounding the wolves that live in the West. It appears they were on the endangered species list, then off it, and are now back on again. The reason their "endangered" prefix has been re-instituted is because ranchers are killing them off again, the same as they did at the beginning of the 20th century. And they are doing it for the same reason. The wolves prey upon their livestock.
The article went on to say that wolf populations in the Great Lakes area are faring much better, and that the many reasons range from an overpopulation of white tail deer to more tolerant "educated" city folk who think saving wolves is cool.
So what it boils down to is that in the West the ranchers don't like wolves because they eat their livestock. Other than that I don't think they have a problem with wolves just roaming around.
So here is my ingenious (or just regular genius) idea.Find an inexpensive way to tag the cows (or maybe just the leader of the herd) with a device that emits a high frequency whistle that would frighten the wolves away but not be perceptible to the cows! 
Dogs hear in the range of 64-4500 Hz, cows hear between 23-2500 Hz, so it should be possible to have the frequency up around 4000 Hz that would work. It could even be a chip of some sort implanted in the cow (if they were inexpensive enough to produce) or maybe a collar that one or two of dominant members of  the heard would wear. Doesn't that sound like a good idea? Wolves would find other things to eat, and ranchers would be happy.
Or maybe the better way to go (in terms of expense) would be to tag the wolves with really low frequency transmitters that would alert the cows but not interfere with the wolves. If the cows were warned, and the wolves rarely successful, then maybe they would start hunting their natural prey. What do you think? Or do you have a better idea?