I use Sevin Dust (read the directions, though, because I've never used it with an outdoor pet). I also use monthly flea gel on our cats (indoors and out).
If spraying pesticides and other insect killing solutions did not work for you then my advice is to use pests traps.There are very good pest traps that you can use and you can even make your own.Visit the following site for info
Ortho makes a pesticide that you can use a spreader to distribute. I forgot the name sorry, but read the bag. It does not have to be watered which is why we use it. It not only kills the fleas, but everything else. For the dog, use those drops that can be placed on their backs. Good Luck, we have had the same problem.