I isolate the OBD socket with a hidden switch. The fuse for the live feed is in the fuse box behind the glove compartment and a fuse switch is available on ebay. Locate the switch in a place of yout choice. Also I made a blanking plate to cover the socket, held in place with security screws. No doubt the low life can find a way around it but it might slow them down. A more satisfying method would be a device that would remove a digit or two and spray them with red paint but the human rights people would object.