How do you stop rusting if an iron object is already underwater?

[Mr-Keroro]

I have a bit of basic knowledge on rusting and corrosion of iron but I am trying to find ways to stop rusting. The problem is what if an object was already submerged in water? Is it still possible to stop it from rusting? I know there are 3 ways of preventing corrosion but I am not sure if there are more. There is Galvanisation, Alloying and simply applying a layer of paint over an iron or steel object but will any of these methods work if the object is already underwater(around 1000m below sea level)? If not then, are there any more methods which could possibly slow down if not stop rusting?

 

[gulfcoastfella]

I assume that in your list of preventive measures, you're including sacrificial anodes, like one made of Zinc for example.

 

[DrStupid]

If not then, are there any more methods which could possibly slow down if not stop rusting?

How about active cathodic protection? In seawater you might need an additional protection against microorganisms.

 

[Bignose]

You could wrap it tightly with something like latex or rubber. Some epoxys might cure underwater... perhaps with a UV light.

 

[Pkruse]

Go explore the many coatings designed to be applied under water. I only have experience with the epoxies, but there are others.