Polish is basically a cutting compound that shines paint by removing the oxidised top surface. You mean 'coating'. Some people swear by it. I simply use Autoglym Hi-Def Wax. But there is a new type of invisible, flexible plastic paint protection film to cover vulnerable parts of a car's body to protect against stone chips, bird lime, etc. Plastic film rather than a liquid coating: www.invisiblepatterns.com; www.5starshine.com