I'm suprised no one has mentioned Diatomaceous Earth yet. We dust with Food Grade DE at the first sign of fleas. Food grade DE is found in human food products such as wheat flour to kill small pests while in large storage facilities. Anyway, DE is not a chemical but rather 80-90% silica. It is fossilized remains of hard shelled algae. Most people think of pool cleaner/filters when they hear DE, but this is not, I repeat, NOT pool grade DE. Only use food grade!!! Order from amazon or other, I haven't found a store that carries food grade, pool grade and garden grade only.
We dust the whole house, rugs, hardwood, corners, under furniture, etc. Then we dust Ellie's crate, under, around and inside Ellie's crate. We wash all bedding, line dry, then dust with DE as it goes back into the crate. We also dust the dog. Not too much because I think it irritates her skin a bit, but mostly just in the areas where we see fleas.
Please wear a dust mask or hankercheif over your mouth and nose while applying DE. Although not harmful to humans if ingested, breathing it can irritate your lungs for several hours after breathing. ALSO, DE becomes inactive when wet, so make sure everything is dry when using or it won't kill the fleas. The silica works to cut the exoskeleton of the flea (or other hard shell bugs) effectively dehydrating them to death. We also sprinkle DE throughout the yard and garden (we are also organic farmers, thus we don't believe in using toxic chemicals, especially on our dog). DE also kills garden pests if hard shelled, but also the beneficial hard shelled insects. So we use very sparingly. Fleas cannot become immune to or resistant to DE because its not chemistry, its cutting their shells!
Sorry this is so long, but I wanted the information out there that you don't have to poison your beloved dog or your family!!