Get a chain lock, wrap it around either the seat pole or part of the frame for storage/transport. There's basically nothing that can go wrong, and there's chain

Get a chain lock, wrap it around either the seat pole or part of the frame for storage/transport. There's basically nothing that can go wrong, and there's chain locks in a wide variety of costs/security. The kryptonite series 4 is well regarded and I personally like it, there's a bunch of good choices though.