You could get rid of the cotter pin completely and close up the wide spot in the mast slot (gate) with a couple of pieces of aluminum plate screwed to the side of the mast. Don't close it up completely, just narrow the opening down to the same width as the slot in the rest of the mast. Your sail slides will drop all the way down to the boom when the sail is lowered. This will also allow you to reef from the cockpit without removing any of the sail slides. Of course you will have to remove the aluminum plates if you remove the sail, but this is a small price to pay for the convenience of reefing from the cockpit.