Treat the area, not the dog. The Frontline is doing its job, your area is infested with fleas. The Frontline IS killing off the fleas which come in contact with your dog. So go get yourself some Diatomaceous Earth (not the stuff you use for pools, that has chemical additives which may be harmful to the environment etc.) get a big bag from your local nurseryman. Go get a face mask to reduce the possibility of acciendtally inhaling the powder. Apply the powder to your yard. Walk your dog elsewhere for a couple of days. The problem is that wherever you have your dogs, there is some other animal dropping flea eggs in the area as well. As long as those other animals, be it tame or wild, you will have a flea issue. Reapply the DE after a rain.