Oil rigs use alot of anodes placed stategically on the structure under the water. And works through electrolysis and it will rust through the replaceable anode plates before it will rust the structure of the oil rig.
Not just on oil rigs they are used on various stationary objects in salt water.
Those are just replaceable plates.
I used to be a commercial diver, when I found out about those.
The electrical versions, work through electrolysis also and if done right should work. But with good under body coatings and using a car wash washing salt off every once in awhile you will not see much rust.
Well unless you have a Chevrolet product.
There is always slot more rust on a Chevy truck then any others.