Anti theft devices

I never locked any of my converts, never left anything of value in them, roof got slashed once outside a bar I frequented, but nothing else.
I used to own a Subaru with a manual that the shifter handle had broken off. I used a 1/2" deep socket on a 6 inch extension as a substitute, just put it in my pocket when I parked the car, could leave the keys in it, nobody would have been able to take it.