Locking gas doors are pretty pointless these days, unless you're worried about someone giving you the sugar-in-the-gas-tank treatment. All cars made for the last several years have anti-siphoning measures built into the line to the gas tank.
Interesting, thanks. My understanding was wrong -- I thought the automakers were using actual metal mesh screens to block the passage of siphons. Apparently (according to the GasTapper video I just watched on YouTube) you can just ram the smaller hose right through the obstruction.
And thank you. I wasn't even aware gas tanks had security measures, let alone gadgets to circumvent it until your comment piqued my interest. Pretty interesting.