Recently fitted on of these to my battery, and it works a treat. http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=320889990833&ssPageName=ADME:L:OC:GB:3160 Really simple idea, but as often is the case, its great. I've got a replacement lock for my engine bay that takes a key, (unlike my current un-lockable one). So I think the two together should do the job great - the only way they will get the bus started is by breaking into the engine bay. The switch is very easy to fit, and really easy to use. Just un-screw and take off the knob and the battery is disconnected. It does come with a fuse link which allows a small current to alarms, clock, radios etc, but it won't take the current required for ignition. It also comes with four 16Amp fuses. The screw knob connects back up really easily too, so no long time spent in the engine bay when you want to set off. Also great for when the bus is laid up for weeks at a time and you want to disconnect the battery, simply unscrew the knob and open up the fuse link. Simple, but effective, 10/10!