When I feel necessary, which hasn't been often, I use Advantage on the dogs and cats, even my barn cats and I don't have fleas. I think you have to be careful with the collars, especially with cats because the clean themselves. I put one on a young cat once, she was about 8 months old and it made her terribly sick. Took the collar off and she was fine in less than 24 hours. We live in the woods and thank heavens, we haven't had a problem with ticks.