Oh how terrifying! My parents is built into the wall, to the left of the sliding glass door, which opens from the right side, so they wouldn't need to worry about that. A strong argument for getting the doors that go into the walls instead of the ones that go onto doors.
What ended up happening?
Being "locked up" and away from everything, seems the only thing he wanted was to feel "human" again by being in a real home oh, and a beer and a cigarette! Fortunately he really couldn't take anything because he had no way of taking it back to a cell. The solution to that was to just install a lock higher up the door that was out of reach, it really is not so easy to get in those doggie doors unless you are a small person. As we all know, almost all homes with a Sheltie security system in place will NEVER allow this entrance!
In over 6 years of having the doggie door, it was a one time occurrence with no other problems, just wanted you aware that it is a possibility.