Before vacuuming, pour a half-cup of moth crystals onto an area of flea infestation and then leave the crystals in the vacuum bag until it is full. It will kill fleas and any insect vacuumed.
I buy a bag of the lavender moth tablets at any discount store. They have two tablets in individual packets. I put a packet in my vaccum everytime I change bags to kill any critters I vacuum up. The lavender oil smells good too.
You can make a terrific flea repellant if you steep a quartered whole lemon in a pint of boiling water overnight then spray lightly on dogs back, hind quaters and on belly between front legs. You could probably also make it with two tablespoons lemon concentrate and one quarter tsp. citric acid to a pint of water.