I have an interesting anti-theft device. My truck is in back of my house outside all the time. Just to prevent 'unauthorized use', I drilled the park brake for a master lock trailer hasp lock. Put it in, and lock, and the drum brake on the tranny is locked solid.
Perhaps a 'club' would work for you. Just enough hassle that no one would bother. I had a guy in my office who had a 15 year old clapped out honda who used one. I one day asked him 'why bother?' That gave him pause for thought.
