Our generator just sits on a pad in a spot in the back that meets the requirements of the various applicable codes and the gas line to it and quarter-turn shutoff are right there next to the generator. It's all exposed and I suppose anyone could come by and tamper with it. But that's how most locations are. Drive behind any shopping center and the gas piping is all right there, sometimes with taps installed so that a trailer-mounted generator can be towed up and attached. (A lot of Walgreens and CVS Pharmacies appear to be designed to be trailer-generator-ready. That's why so many Walgreens and CVS Pharmacies were open right after the hurricane on Long Island blacked out the whole area. Near us, for days upon days, you would drive up the pitch-black main street with no streetlights or traffic lights working, past pitch-black shopping centers, and then you would come upon a Walgreens in the middle of this nothingness lit up bright as day, with everything working inside, as if nothing had happened. Good pharmacy chains take disaster recovery seriously, because people need their medicines. And then they also become suppliers of essentials, like this one did, with cold milk and frozen items readily-available, because they had brought a trailer generator of sufficient size to power the store at its normal electrical service level.)
A friend of mine owns a hardware store. He has a 12kw Onan generator outside his store. He has built around it and the gas piping a very-attractive black wrought-iron cage, anchored into the concrete, that is locked and can be opened. It deters any tampering while still looking nice and not interfering with the operation of the generator, as there is probably 12" or more distance between the generator enclosure itself and this wrought-iron cage.
I'm thinking that you may be required by code to have more fittings than you imagine at the generator location. There is a way to do it right and I'm not sure that you want to be reinventing the wheel on this. For example, most generators run a thick, flexible, not-quick-disconnect hose from the galvanized piping gas line to the generator, to absorb vibration, but it's a "permanent" hose (until you replace it, of course).