I was bathing Paddington over the weekend, and found one flea on his belly

Our basset hound got fleas ALL the time, and I cannot stand them!!!! I flipped out, and searched him several times over, but didn't find any more.
He's on revolution, but I forgot to put it on him last month, with the moving and everything. Now I can't find it anywhere! Who knows where I put it (I'm suspicious that my fiance accidentally threw it out.) We had no flea problems until now, and I know that it is because I am late putting it on him. Urgh! YUCK
By the way, my vet said that it is bad to use over the counter treatments on the fleas because it is making them more resistant to the prescription treatments like advantix and revolution. It's kinda like creating super bacteria, only with fleas, because it isn't really strong enough to do away with all the fleas- the ones that survive become stronger
-O