I've been using Frontline as per instructions but my dogs are covered in fleas following a stay in kennels. The woman in front of me at the vets tonight had exactly the same problem and the vet nurse said the fleas seemed to be developing a resistance as they'd had several people in recently with the same issue.
IMO it's a complete waste of money plus it cost me £60 at the vets for a different flea treatment and spray for the house. I'm having to boil wash my bedding and will have to spend tomorrow hoovering and spraying ð??¡ð??·