We have dogs and cats and have tried numerous medications and treatments to no avail. Finally, I talked to a friend who has been living in Germany for a few years and she said fleas are practically non-existent where she lives. They don't use any chemicals, but the animals never go outside (in a condo) and they vacuum daily. So we kept our dogs in our sunroom and vacuumed twice daily for about 2 weeks, only letting them out to do their business. Sure enough, just by vacuuming up the flea eggs and keeping the dogs inside (away from the fleas outdoors), the problems went away. The fleas in the yard either died or moved on, and the ones indoors got vacuumed up.
I'm not sure if it's a european thing or what, but she says people treated her like she was dumb for wanting to treat her animals with chemicals when all it took was a thorough vacuuming.
Ever since, we vacuum the house daily and have had no problems with fleas. It's going on 3 years now with no expensive flea medications and no fleas. Vacuuming daily was a pain at first, but you work it into your routine.