Constantly scan the yard when mowing (even if it is a weekly yard) because homeowners do some stupid things. You never know when there is a root sticking above ground, a rock, brick, grounding rod, rebar, etc. hidden within. Usually won't have this problem if the client has been with you a while or take a walk through. I have had countless guys mindlessly mow and bend a blade or something stupid. Just some common sense I guess.