Does your vehicle have a locked gas cap? Mine does not but I want to get one. Someone is stealing gas in our area. Sick! Gas is expensive ... I get it. I don't want to have to buy it twice! Can you get a locked cap?
My first car had one, you could unlock it with the car keys only but now that I have another car, well.. I just have to be careful. Maybe you could have it custom made, it will cost you but in the end it's worth the trouble.
You can buy locking gas caps on Amazon for as little as $10.00. The key is in the middle of the cap. However, they don't appear to be that hard to get off without the key. You may want to consider one that attaches to the car itself. That will be more expensive.
