I’m a big proponent of diatomaceous earth since it’s nontoxic. Also, if you live in a humid area (like I do) then a dehumidifier is a great purchase because fleas require a certain amount of humidity to live and actually hatch from eggs. A dehumidifier is just good in general if you live in a humid area, so it’s a double win!
This article goes into some other interesting options like pennyroyal plants as a sort of flea repellant. It lso suggests trimming outside areas that could foster fleas. https://happypetlabs.com/blogs/happy-pet-tips/how-to-get-rid-of-fleas-on-a-dog-fast
