After giving my son some boat driving lessons on the Minimono, he managed to crack the hull.
After going home and thinking about it, I rummaged through the plumbing stuff I have in the Mancave and located Premium ABS cement used for plumbing that I bought from home depot. Using a toothpick as an applicator, I glued the crack and used a couple of elastic bands to keep the crack compressed while it cured.
Next day I took it back to the pond. 100% watertight. It's not pretty, but very effective and easy.