On my old fishing van I fitted a tap behind the seat, used to just shut it off before leaving the van when parking it in isolated places. Made it out of copper tubing, being diesel the fire risk was minimal, you can get the remote fuel stops and note Franks comment about cost but, IIRC they were not too bad?
Years ago I used to design, build and install anti theft devices and came to a pretty good conclusion. If your car was stolen and then parked in a busy area, unless it had a tracker activated it might not be found for months, or simply stripped and never seen a again. Most alarm systems have some kind of weaknesses that can be used to steal your pride and joy. So I built fuel/ignition shut off devices that activated AFTER the vehicle was stolen (assuming the usual systems had be circumnavigated), there would be a timer that would be set according to the owners home location.
For example, if you live in a property that was a mile from the nearest main road then and it took say 2 minutes to get there, then the timer would be set for two minutes. The idea is the thief has bypassed your commercial or OE system, and is now driving your car (and perhaps even eating your mint imperials from the centre console!), at or very near the junction the car shuts down, he (or she) will not want to be faffing around exposed to the general public trying to find out why the car has stopped and ANOTHER alarm is sounding with the lights flashing etc. Of course it is even better if the vehicle is causing a disruption/jam, the police will be on the scene pretty quick.
Just a note, a remote fuel stop fitted at the tank outlet (remove centre seat and oval plate for access), would get quite a bit of attention as the thief was throwing out your seats?

, hidden switch (reed switch BEHIND) dashboard and needs a magnet to energise and yet nothing to see or fiddle with. ....yeh sad I have built these, I have a great imagination, remember a comment I made awhile back, it was not a wind up, you really DID need to squeeze the sun visor to get my Corsair to start!!
regards
Dave