I think nowadays an old car with a manual choke, a stick shift, and a separate coil where you can remove the ignition wire between the coil and the distributor would probably eliminate all theft outside someone just picking the whole thing up with a rollback tow truck. ;)
just remove some fuse that you know for sure prevents car from starting (fuel pump fuse for example) and you don't need to disconnect any wires.
sure, you will have to spend additional 20 seconds removing and putting it back every time, but it is simple and safe, unless thieves are willing to go full troubleshooting on why car doesn't start in the middle of the night
