You need to find a product that uses "Nematodes" to get rid of fleas. This is a natural way of getting rid of fleas and doesn't poison the pets or the plants.
Nematodes are bugs that live off of eating fleas. Their ONLY purpose in life is to eat fleas. Once the fleas are gone they die. It is an outdoor only product for the most part. One company that makes is Bio -something?. Can't remember the last part of the name off hand.
This product is difficult to find. It comes in a can similar to the type carpet freshener is sold as. It sprinkles out. You may be able to find this at Pet Stores or possibly a Home Improvement store. If no luck there then try the internet.
I also recommend adding Brewer's yeast to the animal's diet. It helps with the coat, shedding, and fleas. I agree completely the stuff at the Vet's office works the best. My dog Scooby is allergic to fleas. I've had to feed him Benadryl quite often if he gets bitten. I have to keep a can of the Carpet Flea killer on hand as well.
Hope this helps and good luck!
Scooby, Shaggy the "Dogs", Ms. Thang the "Cat" and introducing Measley Weasle "The Ferret".