Have the house bombed for fleas. So it kills them all in all the little cracks. Also adding raw apple cider vinegar to his water will help. It makes his ph more acidic and fleas dont like it and as he is getting older its good for his joints.
http://www.earthclinic.com/Pets/acvfordogs.html
It has to be raw not the stuff in the supermarket next to the salad dressing. If there is a whole foods by you they will have it.The company that makes it is called Braggs.