stopped my car getting nicked in nottingham about 10 years ago by putting a simply switch under the seat that interrupted the fuel pump, almost the same thing as the fuel pump kill switch as it was in the wiring for that

they were pushing the thing down the road after breaking the steering lock and window and pulling the indicators out and fucking the door locks on my 3 door but they couldn't start it as i put that little switch in the way

bit of faffing about under the seats to reconnect it again but well worth it when all else fails

got a battery kill switch on the mondeo too which lives under the bonnet, so it's keys to open the bonnet then key to turn the battery on

after which there's the factory ford alarm AND the cat 1 alarm to deal with, both of which immobilize different circuits on the car depending on how you open it

plus it lives behind a security post and metal gates so it's a right pita to get out of on any normal day, hence me not using it as much