You're going to need a pest control plan for this, the fleas are probably sand fleas, and they are not easy to eradicate. I used to spray the lawn and oyster shell driveway with Liquid Sevin once a month, and I also applied it indoors.
Read the label carefully and follow all directions. It used to work very, very well but it is a bit pricey. Still, bang for buck - it rids your house and yard of not only fleas but roaches, slugs, earwigs, and several other pests. Set the spray nozzle on the 'fan' setting to get an evenly distributed spray pattern.
There are other remedies like dichotomous earth, and boric acid-cheaper but not always effective.
Can't stress enough that you need to read the label and directions VERY carefully to be sure you mix and apply the spray at the correct dosage and time of day, Sevin WILL affect honeybees and you don't want that!
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