Right, someone's nicking petrol out of my car. I first noticed it a few months ago when I had my van and this last lot of petrol has disappeared quick, the flap was open this morning as well. A locking petrol cap is the obvious answer but it's a twisty one that's going to be a pain (but not impossible) to buy, but in the meantime, what can I do to deter petrol thieves? Sleeping in a nearby bush is not an option[1] and I did consider dog shit and / or razor blades on the cap / flap but this will inconvenience me as well. [1] Nor is moving to a less pikey area.