I really personally think that fleas can get used to a certain treatment. I used advantage for years & years since it first came out & now this year the fleas are not terrible but they are there. They have never been there before. So I switched to Frontline & thats keeping them away.

I suggest switching to another reputable brand like advantage, frontline plus (if you used just frontline before), revolution or advatix (but advatix can be bad for cats I don't reccomend it for homes with cats).

The important part is to make sure NOT to mix different brands like you have been doing. I would not add anymore chemicles to your dogs system, wait until he is due for his next dose of frontline (1 month form when you applied it) and give him a good bath before applying something else.

Have you tried treating your yard? That can help a bit too. Just make sure your dogs stay out of the area for at least 24 hours (or whatever the product reccomends, some types you should wait until a rain)

good luck, fleas are no fun thats for sure