I wonder if you could at least do something petty, like swap the +12v and GND pins with the Bus+ and Bus- pins on your OBDII connector so it would fry their fancy tool when they tried to read your data.
This also makes it impossible for other mechanics to diagnose and fix your vehicle. It also makes it much harder for you to use that port to diagnose and fix the vehicle yourself with readily available tools you can buy. The OBDII port is a blessing, not a curse. There are things you can do to limit the telemetry (this will be on a case-by-case basis for the vehicle and manufacturer, so I'm not going to detail specifics) but that is one of the sillier things you can do.