On DIY security, there’s an old budget motorcyclist trick that might be adapted.
The standard motorcycle seat is vinyl covering foam, with a base of hard plastic. There’s also usually a small amount of space just below the seat.
Here’s the trick: get a block of wood, sized to fit snugly in the gap beneath the seat. Drill a hole in the plastic base, directly beneath the rider.
Put a nail through the block of wood, sized so that when you put it under the seat (with the nail through the newly-drilled hole), it stops just short of penetrating the vinyl seat cover.
Guaranteed perforated perineum for anyone who sits on the bike. Disarm by removing the spike block; some sort of visual armed/disarmed reminder cue (loop of bright wool on the handlebars, etc) is advisable if you want to avoid self-inflicted embarassment,
