Anti-theft switch on ECU - possible?

I am considering to fit a hidden anti-theft switch in my D90 /td5.
I already have a LR genuine alarm and do not wish to cut all 12v supplies. So a battery switch is not an option.

Has anyone incorporated a switch to the ECU de-mobilizing the vehicle without harming the ECU or cutting vital 12v supplies ?

Any ideas?

Lars

I did something quite similar but on a D2... i'm not familiar with Defender diagrams but as an ideea, if u want to make it unstartable there are many possibilities... the easyest ways are:
1. a switch on the inertia switch's circuit(normaly opened)
2. a switch on the main relay's coil circuit(closed)
3. a switch on the starter relay's coil(closed)
4. a switch on the fuel pump's feed(closed)
......... and so on

Disable the crank position sensor and the engine will never fire. Even plugging in another ECU with all security deactivated wont get the engine to run as it has no idea when to fire the injectors.

There's hundreds of things you could disable. It's remembering to do it every time! Cos you can guarantee the one time you don't.....................

Thx for the ideas here! Well if I use the inertia switch then I would have no risk of damage right?

putting a switch on no matter which circuit will not create any damage whatsoever