We've been besieged by an infestation of fleas from some unknown source. My father sprayed the yard and lawn and shrubs and everything around the house twice in 30 days with flea and tick killer. My mother laundered all the dogs bedding, bombed the garage, bombed the house. We've bathed all the dogs in flea shampoo, sprayed them with flea killer, and two days later we still find about 20 healthy blood-lusting fleas on two of the dogs!
So we gave them all Capstar and that seems to have done the trick. But I've never seen such a persistent flea problem. They have to be coming from somewhere, the fact that my mother brings a new dog home from the pound every two days doesn't help.