When I lived at sea level fleas were a constant horrible battle. but after moving to high altitudes, No More fleas at all.
Down south I battled them on every level: wipe them out treating floors and yard then keep property eradicated.
Initial flea killing baths & rinses to initially wipe them out on animals, then flea collars for protection. This was before they started making the skin drops & oral stuff.
If your grounds can't support fleas it helps a whole lot to minimize what the dog requires.
I never experienced any reaction to flea collars on cats or dogs. cat in previous post with raw neck must've been allergic, which can happen with almost anything.