We are in Florida and some years fleas are terrible in the summer. We use either Advantage or Frontline when we start to see a few fleas, and re-apply when we start to see fleas again, usually about every 6 weeks through the summer and fall. I have used it on an 18 year old with no problems. I feel that the problems fleas can cause outweigh the occasional use of a fairly benign chemical, and certainly keep the dogs more comfortable!
If we lived where fleas were not a big problem, I would try some of the more natural remedies.
Anne in Tampa
You have an 18 year old? Wow how is he or she doing? I had a Tri color many years ago live to be 17-1/2.