[quote=Christo]On our own dinghy back in Blighty we have an engine lock also, which prevents the engine being removed from the transom. I've never seen one on a charter dinghy...which would make pinching one of those shiny new Yamaha 15hp engines incredibly easy.[quote]

Christo brings up a good point. Usually the lock and cable supplied by the charter company is long enough to secure the dingy, engine, and fuel tank to the dock.
Just loop it through something metal on each that can't be easily broken.