Pardon me, this is my first post ever and I haven't figured things out yet. SERGIO: Working at a veterinarian's office for a number of years (though a long time ago), I can confirm that fleas do not need to live on the dog (or any other animal). In fact, it is quite possible to have an infestation of fleas in your home even if you have no pets at all--they can simply hitch a ride into your home (or car) on a pants leg, sock, etc. Then they will jump onto any warm blooded body (including humans) for a meal. This happened quite often when we would have a very wet and hot summer. Fleas do indeed take up residence just about anywhere so, when treating the animal, it's necessary to treat the residence, the furniture, etc, paying particular attention to where the dog sleeps. You could, for example, treat the dogs with DE or even a heavy duty insecticide (yuk), but it would be useless unless the dog's bed, couch, cracks in the floors and such were also treated.
I didn't know about DE back in those days and we haven't had pets in quite a few years, so I can't verify that it works on fleas from my own experience. However, we've used it often in garages, basements, storage units, sheds and our home with excellent results. I believe the key to success is to use it liberally and repeat the application fairly often--especially if it gets wet. I have heard that it can be used directly on the animal, as well as in the animal's bedding. This article might be helpful--it's long, but may be useful to you:
MotherEarthNewsArticle
Note that she mentions avoiding organophosphates and carbamares--these are very dangerous chemicals and are even more dangerous when combined (such as spraying on an animal and then having the animal wear a flea collar). It actually increases the toxicity enormously. She also mentions pyrethrins. We used pyrethrin shampoos on very young puppies and kittens when they were badly infested with fleas--a severe flea infestation can be very dangerous to a tiny puppy or kitten. I've never tried anything with d-Limonene, which she says is natural. It might be worth doing some research on it. But I would definitely try the DE first, which she recommends and she gives a 'battle plan' for tackling the fleas.
I hope this is helpful and you win the fight with the fleas, they can be a real challenge. In my very first apartment, as a teenager, we had several cats and, naturally, my roommate and I ended up with a terrible infestation (the fleas loved our shag carpet!). It was horrible--so bad, in fact, that my roommate wore flea collars on her ankles. We had no idea back then about the dangers of the chemicals involved.