Protecting fuel tank from theft

Thanks for all your info. Drilling fuel tanks is happening here by police reports and car dealers complaining. It is parked in a safe place in my yard. The thieves don't care they steal lawn furniture right off your deck. The Sewage sticker is a good idea. I thought of putting an outside cover of stainless steel. Please note I am in one of the better areas of the city. At $8.55 a gallon for regular gas some will do anything