Dave's right. I think just throwing the cover over it is probably 98% effective, but if you want to go "all-out" you can take the five-step approach. All but the QR and ignition kill switch are something you can throw together this afternoon. BTW, the green knob on the battery disconnect switch either loosens, or comes completely out, to break the circuit.
1) Put a cover over it;
2) Have a quick-release on your steering hub and remove your wheel;
3) Have a hidden "kill switch" for the ignition;
4) Have a quick disconnect on the battery;
5) Cable lock your wheels to a pole.
