My wife and I got tired of Kasey rocketing downstairs and trying to run through the screen door & either ripping it, or knocking it out of the tracks. So we ordered a plastic snap together dog door. We had to modify it because the snaps didn’t fit together well, and kept coming undone — I drilled through the plastic on both sides where the snaps were, and we sewed it on with weed whacker line. It’s been in place three years now and it’s doing fine.
Even without the kit however, you can see how it would be easy to make one of these with leather, wood, or plastic strips, and some fishing or weed whacker line.