I make it a habit never to touch the interior door lock controls. The car will lock itself once it gets going, and when I leave I always use the key fob from the outside.
On my old car that didn’t have a fob, I tried one of those magnetic things that fell off. One of the structural members underneath was hollow inside, I tied a key to some wire and put it inside, impossible to see but able to fish out since I knew where it was.
For newer cars, I second the suggestion to get a chipless key cut and find a place to hide it. If you’re worried about completely loosing your key, get a dealer key made and programmed, cut the metal off, and hide it someplace inside. If you loose your key tape the two together and you can move, a car thief finding both “half-keys” is rather unlikely.