I've been around anodizing for decades. That's why I'm surprised that it wasn't effective in this application. Maybe seawater electrolysis defeats the anodizing. If I still had access to a lathe and mill, I would have whipped up a pair of these in 316L stainless!

Whenever i run into such issues adn eventually solve them I simply tell the wife, "I Win!"

those hunk of zinc are called anodes for a reason...