I had one zipper that would go past the 'all the way open' end, I sewed that shut with 8lb test line. I had another where the stop at the 'all the way closed' end came off. I put a drop of super glue (or equivalent) on each side and sprinkle baking soda on the drop. That will turn hard as a rock almost immediately. I think the gel type glue would work better next time but I didn't have any. Fortunately, the drop I laid down was enough that the traveler stopped at the end.