The last time I had Revolution "not work" it was because I was depending on it to do too much, I think. It killed the fleas on the dogs, but not in the environment properly. Ended up evacuating and bombing the house, Capstar weekly and switched to Seresto on the dogs. Much better now. Revolution is a good maintenance tool for our fosters but if they come in with fleas, I Capstar as well. It's too bad because Revolution is so expensive, but it does other things well, so I guess I shouldn't complain that much. But in the future I don't think I will recommend people using it on dogs. I like the Seresto collars a lot