I have been using Advantage for about 3 months on my 1 y.o. cat and he still scratches quite a bit. I'm a little concerned because I like to let him go out in the yard with me every once in a while but not if he's going to get re-infested. I thought that Advantage protected against this?? However, even on months when he's stayed in the house, he's still scratching. Any ideas on what else to try?