I put a locking pin in my pop door to guard against predators fashioned with nail on a string or in my case heavy nylon whipper snipper line. The locking pin is drawn in to position by permanent magnet(s) inside the locking cavity in the frame of the door { I am currently only using one magnet on my small door}. You have to tie a not or a bolt to serve as a check once the pin(s) are drawn away from the magnet(s) against a bottle neck in order for the door to be pulled into position. I got magnet(s) from old speakers in a scraped car make an easy and effective locking device. My guillotine style door is raised and lower with this same type of line with just a small hole drilled at the top of the coop man door in my case. The reduced friction on this heavy monofilliment line means you do not have to bother with pulleys and the like. The pop door raises with little to no resistance with a gentle pull and falls with just the weight of the door which is made of of just ½"plywood. I hook the loose end of the line with a carabinerto the wire panels in the run in the open position and just unhook it and let if fall to the closed EASY PEASY.