The simple answer is there is no guaranteed way to prevent you from screwing up. It's up to you to be aware, keep gasoline in an easily identifiable container, and don't put it in your diesel tank. If you carry cans with gasoline and diesel fuel, and are in the habit of adding fuel to your truck from the diesel fuel container, it's pretty much assured that you'll add gasoline to it instead, at some point. I think the easiest thing to do is make it a habit never to add fuel to your diesel vehicle from a container other than a fuel pump. That would help, but like I said: "No guarantees".
