Berkeley has an institution, Adventure Playground.

It's a playground where kids of all ages can get hammers and nails and wood and build whatever they want (with adult supervision).

It's a wondrously emergent place, totally resonant.

It also has an internal balancing set of incentives.

To get a tool, you have to find 5 loose nails or "splinters" of wood and turn them in.

If you find a "Dr. Dangerous" (a piece of wood with a nail sticking out the other side), you get 5x the reward.

They have magnets on a string that you can pull through the sand, finding loose nails to turn in, that even the youngest kids can do.

This creates a clever and stable equilibrium where the kids themselves are keeping the playground in a stable, mostly-safe state.