Don't forget about the good old flea comb. If you think you are picking up fleas when your dog is outside use the flea comb on him as soon as you bring him in. Many times when the flea gets down to the skin you cannot see it. You will be amazed what that flea comb can find that you had no idea was there. You can put any fleas that get caught in the comb in a dish of water with dish washing liquid in it. The comb may also pick up some flea eggs. The eggs look kind of like a partially clear grain of sand. Fleas will lay eggs on an animal but they love all the cracks and crevices they find in your house, too. Flush anything you get in the comb. Once your indoor situation is flea free and under control the flea comb will help keep it that way. The comb will also detect ticks.
I feed some feral and homeless cats in my area. (Outside) I have checked the ones that are tame enough to touch to see if they have signs of fleas. Strangely they do not. All I can figure is that indoor animals tend to get more fleas because the fleas can multiply so quickly in a contained indoor environment. Maybe the feral diet has something to do with it as well.