Many, many, years ago, I saw a unique solution to a problem of sand and salt air getting into a door lock on a beach-front vacation house.
Owner had taken the lid of a large (1 qt, approx.) jar and cut an opening in it so that the lid fit between the lock and the door. When he was leaving for the week, or whatever, he screwed the jar onto the lid, thus covering the lock. I have always thought that was a slick solution to protect seldom-used locks.
Just thought I'd pass this along in case there's someone out there who hadn't seen or heard of it before.