Michael Amundsen, esteemed fellow designer, suggested a different object of the game. Get all your checkers into a contiguous stack, possibly with enemy checkers above and/or below it, anywhere on the board.
RG's initial impression: "I think his suggestion might work. Not sure. The game is a lot more complicated now." Based on that appraisal, I will change Silo to incorporate the new goal. I'm going into the countryside for a few days and I'll make the change when I return.
Normally I'm not one to tweak a broken game, opting instead to simply withdraw it. But I really like Silo - even more so now with what seems to me a more elegant object. I put a lot of work into the graphics and programming... and the game design itself. I discovered the mechanism in a matter of minutes, but this was preceded by many unsuccessful attempts over a span of many years to design such a game. I finally got lucky with Silo, stumbling onto something that works (or rather will work, with any luck).
So why not? Keep your fingers crossed that the new version holds up. Ultra simple games don't come with a warranty.