Obviously no wife/girlfriend is the best scenario, but if you are already married and it's cheaper to keep her, a great strategy to prevent her from cheating or trading up is to tell her to stop shaving her legs. Say that you love her for her, not just her looks, and she doesn't need to go through the trouble. She will become way to insecure about her legs to cheat.

It works too if your you're going to be away from each other for awhile. Tell her you don't want her to shave her legs while you're apart. If you come back and her legs look like they've been shaved, it means she shaved them for someone else.