Someone asked me about my Variocage, and how I solved the problem where a small dog can get their head out the corner. (or a larger dog can get a collar caught!)
I cut two pieces of PVC pipe, just long enough to fill the gap, and slipped them over the last bars. Problem solved! I wish I could take credit, but I learned it on:
Lots of people there have done the same.
The first photo is the crate as it arrived... you can see the problem in the corners. The second photo is with the PVC sluipped over the end bars: