Here's what I did to test this idea:
I bought a 14 oz can of Plasti Dip, cleaned the outside of the carboy with soap and water, then cleaned with rubbing alcohol using a paper towel, and then painted the Plasti Dip (without diluting it with anything) onto the carboy with a sponge brush. The 14 oz can gave me enough to apply four coats to the carboy.
Once dry, I took it outside, placed it in a cardboard box, filled to about 3/4 full with water, then tried hitting it with a hammer. The box didn't allow much room to swing the hammer with enough force to break it, so I decided to try dropping it. The first couple of drops were on the lawn, which seemed to give a little when being impacted by the weight. I then placed a piece of slate under the box, and tried dropping it on that. The first two attempts weren't successful, but I was determined, so I dropped it a third time. With the final drop, I tried to direct it onto the corner. That did the trick.
I quickly grabbed my camera to take pictures of the aftermath. Notice the water level in the box. There were several small holes in the coating that were spraying water out. It won't save the beer, but it will slow the loss down.
Though it isn't 100% safe from shards of glass puncturing the skin, it does seem to add a measure of protection. I will be doing this to all of my remaining carboys in the near future.
