When I was a kid, we had a really bad flea infestation in our yard one year. Because of the weather that year, the flea population was out of control.
It was impossible to keep the fleas off our dogs, who were indoor and outdoor pets. Eventually, the fleas were in the house as well as in the yard. I can remember wearing white socks and looking down to see them covered with little black dot, which were fleas.
We took the usually steps as far as flea collars, powders and spraying the inside of the house. Then we learned that we could treat the yard.
My dad bought some liquid flea killer from the hardware store and mixed it with water. He sprayed the yard once a month and we could see a considerable reduction in the number of fleas in the yard and in the house.