How to get ri of fleas outside?

I live in a rental house and my dogs didn't have fleas before we moved here. I'm pretty sure the previous tenant didn't get the place sprayed. Anyways it's on acreage and it's an unlined liveable shed with concrete floors. On 1 side of the shed there is an enclosed patio area that has a brick... show more I live in a rental house and my dogs didn't have fleas before we moved here. I'm pretty sure the previous tenant didn't get the place sprayed.
Anyways it's on acreage and it's an unlined liveable shed with concrete floors. On 1 side of the shed there is an enclosed patio area that has a brick and dirt/sand floor. At the back and on the other side it's brick pavers then dirt, trees and bush around the rest.
I treat my dogs with the comfortis tablets. The patio area is the worst affected and that's where the dogs were but we'v moved them around the back.
Tried a vinegar/lemon juice spray but of course that didn't work. Just got the place professionally sprayed and he tells us after he sprayed that he used an "environmentally safe spray" as we have 2 young kids. We only noticed a couple that night but 3 days later their back with avengence 😡 The patio area is where we have to walk to come into the shed. Haven't noticed any fleas inside yet. I'm pretty sure the fleas are coming from the other side of the patio area where the dirt and palm trees are. I heard that using other product aswell as a professional treatment will stop the pro treatment from working?
Anyways any suggestion because I'm going insane.
Also a friend said the real estate should reimburse us for the spray but we haven't mentioned anything to them and we have been here for 3 months months.
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