(I would have gotten around to it!)
My first recommendation would be to make him a house dog... And let him sleep in your bed.. But I'm assuming that's not the advice you're looking for ; )
First question is... Are you currently using a monthly topical like K9Advantix, or frontline...etc.? If not, than that's certainly a place to start... If you are, and it's not working, than I'd advise you to switch to another kind. Most of the major brands out there are actually using different pesticides or combinations pesticides. Fleas in different areas become resistant to certain pesticides, so sometimes just changing which product you use can go a long way to solving the problem.
My next question would be... What has the exterminator been spraying.. And is he using the same pesticide each time... 'cause if he is, he's wasting his time and your money? If it's not working.. The fleas in your area have become resistant to whatever he's using, so if you have it done again, make sure it's a different product is used. (pick a topical product for your dog that has a different active ingredient than the one the exterminator has been using!)
My go to product is Zodiac Fleatrol Premise Spray II with Precor... Permethrin is the main ingredient, and in my area it works great. It's a synthesized version of a chemical derived from chrysanthemums... And does not harm most mammals or birds... It has a low mammalian toxicity and is poorly absorbed by skin... But it kills fleas, ticks, flea eggs, and flea larvae... And with the Precor added provides protection for up to 7 months. It a very fine spray that's intended for indoor use, because it's a water-based formula.. however, unless the dust bowl that fido chooses to sleep in gets watered down regularly... It would be a great product to use in and around his sleeping area. I really like it because it has no pesticide smell... And leaves no reside at all when dry... And as an added bonus, one application works to keep ants out all season long! (they can be a major problem in the southwest during the hot summers) I spot use it very sparingly when needed, but it's intended to be used all over every surface of the home (carpets, drapet, furnature.. Etc.) so it seems to be pretty mild stuff, as far as most mammals are concerned. There are also sprays and powders containing Permethrin for use directly on the dog, that are intended to work for about 2 weeks.. I've never tried them, but assume they'd work just as well.
Here's a fact sheet re: Permethrin
npic.orst.edu ... That's all I can suggest... I think the trick is finding out what your fleas are least resistant to, and then hitting them with that... While at the same time trying to do as little collateral damage as possible... Good Luck!