My design is brilliant if I do say so myself (though I'm sure I learned it from this site).
Guillitine door so it slides up on the inside, but I have a rope attached so that I can walk in the coop entry (not in the coop itself) and open and close the door w/o getting poopy.
If you're talking about the entry door for you, it can't open in -- or at least it can't for long, because the poop blocks the swing.