In the 15 years that we had Maxx, we never used any kind of flea product…and he never had fleas.
We haven't used anything on Gracie or Blaze, either, and neither of them have fleas. If we ever do see fleas, our first line of defense would be a natural product of some kind. Only if the natural products didn't work would I resort to chemicals. Of course, YMMV.
Dr. Pitcairn's Complete Guide to Natural Health for Dogs & Cats has information on natural flea products. I'm sure there are other books and/or websites that do, too…just do a Google search.