As more and more people are reporting stolen gas, merchants are reporting a significant increase in the sales of "Locking" gas caps.
These caps may deter some thieves, who move on to an easier target. But locking caps are easily thwarted.
Some tips: Buy a locking gas cap. Even if not a permanent resolution, it is a step toward discouraging thieves from siphoning gas. Park in a lighted area, or in a garage, if possible. Install theft devices that detect motion on your vehicle.
If you have any other suggestions or ideas, please post them here.