Well im having the same problem right now also...i have sprinkled seven dust all in my yard. I just did it a couple days ago. They also have sprays that you can attatch to your hose and spray the yard. I have also heard that you can throw mothballs out in the yard, fleas hate the smell. But i dont know alot of people who would want them in there yard. Its ugly and they smell horrible.
There are several methods you can use to get rid of sand fleas. Some include, use of vacuum. This helps as you can vacuum parts of the garden thus helping get rid off the fleas' eggs and larvae. You could also employ steam cleaning to get rid of them. For more information on the same, visit http://fleasandhumans.info/how-to-get-rid-of-sand-fleas-2/.