Guys, in the last 10 or so years there has been a revolution in flea treatment.
It's called "IGR" or insect growth regulator.
Basically, it's a compound that doesn't let the juvenile fleas mature beyond the larval state. That means they will never reproduce. It only works on the genetic makeup of certain insects, and is totally safe for humans and other mammals.
The catch (if you can call it that) is that it doesn't kill anything, so you still have a generation of fleas to deal with before the IGR starts taking effect.
There are several different varieties we use.
Ultracide- IGR combined with killer. Expensive, but treats areas where the cats hang out. We used it twice in the beginning of our treatment program, and haven't used it since.
Archer- concentrated IGR. We dilute this and spray it on the carpet and in the yard in a 20 foot radius of the house. We used to do it every six months, but now just once a year or whenever we see a flea or two.
Lufenuron- generic name for the ingredient in "Program". IGR that is internally ingested. We give this about once every 5 to 6 weeks (even though dosage says monthly)
Additionally there is "Capstar", an internal formula that kills the fleas as soon as the bite, and also induces them to bite! (This can be either disturbing, or amusing to watch, as the fleas will literally start biting and thrashing in death, which can drive the cat batty)
...and finally, if there is a flea problem, there is likely a tapeworm problem.
Praziquantil is what you want for this, and two treatments about two weeks apart is the best procedure, although we've had good luck with 1/2 the recommended dosage per treatment.
Three years ago we had a horrible flea issue.
We did as I've described above, and have only seen one or two stray fleas in the three years since.
We have six cats (and a chihuahua) that are free to come and go in and out of the house as they please.
We get our generic capstar (haven't needed in 2 years) and lufenuron from ebay for $20 per six doses, and praziquantil (also not needed in years)from Tractor Supply.
Archer and Ultracide also from ebay- shop around as prices vary quite a bit.
It's doable with some effort up front and just a bit of regular maintenance.
All the humans and animals involved will thank you.