Polyurea is a surface coating that is sprayed on and dries in seconds. It is rubbery and sticks very well to metal (concrete requires some preparation and I have seen first hand that it tends to peel off of concrete surfaces). It is very very durable and algae/barnacles has a hard time attaching to it.
It was used for the San Mateo Bridge, the Boston Tunnel, US Marines amphibious vehicles and is starting to be used in a lot of backyard ponds, underground bunkers, roofs, ships and more. Most people would be more familiar with the coating in the back of modern pickup trucks which is polyurea.
Coca Cola uses it for their water tanks
It has been shown to protect against explosions
Sprayed onto boat hulls
fully coated boat
Makes objects water tight