Hi Chris,
I think the key to flea control in a challenging environment is to focus your efforts on shutting down flea replication and not on killing adult fleas. The products geared to killing adult fleas without addressing reproduction can fail because some fleas always seem to survive to reproduce so the cycle continues.
A very effective option is to administer lufeneron to all the dogs and cats in the home.
http://www.jarvm.com/articles/Vol10Iss3/Vol10%20Iss3%20Dryden.pdf
If the above isn’t an option I think a professional application of Fleabusters borate powder is the next best thing. You can apply it yourself but I think a professional application may be more effective. The company guarantees their product.
For adulticide I’d follow your vets advice. I’ve heard in challenging environments some products need to be given more frequently than the label directions specify. An option to consider would be Bravecto which reports good control for up to 90 days after one oral dose.
If my finances were limited and I had to choose between using an adulticide or shutting down reproduction I’d choose targeting reproduction. The adult fleas can be dealt with by less costly options like combing them off or bathing.
