My bi-fold has always fit so tight that it tends to pop open slightly. I have a dog so I need it closed when I don't have her yard setup.
Thanks to Harold "Lee" Greer, at one of the gatherings, I have a lock for it. Lee told me to use a piece of square aluminum stock, 1" I think, and cut one side cut.
It sits on the top of the screen door rame. To lock the door just slight the aluminum piece across the center.
The discolor/rub marks are because I have the center awning
brace stored on the closet wall and the screen door lock rubs on it while underway.