Over here we have a prolific flea population, and different types too, due to the weather. Their eggs can survive for an eternity in dry hot conditions, especially in sandy soil.
Options are to get the pro's in to spray house & yard, they guarantee for a year & use a plant based poison that isn't too toxic (cover ALL fish bowls/aquariums with blankets & remove birds - yeah, I know they say it's not too toxic, but it will knock those off).
Alternatively, we need to think of our pets are the "bait" ... once each flea completes it's life-cycle it will hunt out the nearest dog, cat or human to draw blood. If dogs & cats are consistently treated i.e. every single month, then eventually that cycle is broken, no two ways about it. The trick is in being consistent though.
Unfortunately, those with cats who roam outside have to treat ALL animals month in month out as they're what drag the blighters back to your property. There's absolutely NO POINT whatsoever in putting yourself through all this backbreaking work and stress if there's even a single flea lurking outside your back door and your dog/s go outside to potty 'coz that flea and her few 100 eggs will hitch-hike a ride back inside.