Here's what I did to keep my Boxer from opening the screen door. Went to Ace Hardware and got fasteners that are used to secure old time screens in frames. Simple things really. Drilled thru screen door frame and secured fastener with small bolt and nut, added super glue to nut once I determined tightness, also added a few washers to bolt inside of door to bring out the fastener to correct width to allow fastener to be swung over door frame. Trial and error to get tightness right. I also put fastener midway on door to allow me to access it from outside of door so I could keep dog in the MH when I went outside. My door frame didn't allow for the simple bolt type of lock that I first thought of using.
Here is fastener in the closed position:
Here is what it looks like open, it stores well and does not get in the way of normal operation:
So far the dog has not been able to open door, but I'm waiting. LOL