"Foster" has been hanging around my house for 2 - 3 years now. I can not take him "in" as I have 3 other cats....not to mention that I don't yet live in my house, which is in a nearby city. I have been feeding him and putting advantage on him. I already have the advantage for my other 3 cats, so I put it on him monthly as well. The problem is, it doesn't seem to be working on him. He is covered in fleas. What is a good flea spray out there that will work on contact? And, can you use advantage simultaneously with a spray?