Read in a Tom Clancy book (Without Remorse) that the cathodic protection is for the propeller which was--I think--some combo of zinc and copper. If the electric thingy isn`t kept batterized, the metal becomes very fragile (brittle) and can break if it hits sand.

That said, just drive your car into a pond, let it soak for a while and drive the vehicle out. It works better with a boat, but in a pinch . . . .