After test 12a we added a restraining pin to the test rig. This was done at the suggested of one of our venerated old ones (now a college student) who was visiting for the day. It wasn't subjected to a think through all the failure modes you can think of discussion.
Also, the members at small were spread out about 15m away from the test rig.
These precautions weren't needed; it didn't pop out this time.