Starter disconnect
Go to a boat supply store (Eastern Marine is good) for a boat battery disconnect switch. Then wire it in the starter lead (not the main battery lead) so the alarm, etc. will remain active. This is a little more complicated than it sounds but is easy once you diagram it. The key is to separate the main feed to the instruments, etc. from the solenoid so that instrument feed stays connected to the battery even when the switch has removed power to the solenoid.
Alternatively, put a lower amp switch (20 or so) in the solenoid lead to the starter solenoid.
The more sure the switch, the bigger pita it will be for you to use it.
Either will prevent anything but a tow vehicle from getting your car.