I keep one of those magnets on the boat and another in the garage. I do get stuff back as fast as I can. Otherwise you might as well just let the sea have it.
One thing you have to keep in mind is it isn't really the water that hurts things, it is the air. If you are not prepared to deal with it, you are better off leaving something in the water until you have your WD40 or whatever in hand.
Typically I flush it immediately with fresh water and then hit it with a massive dose of WD40. When I found the lower unit in my boat full of salt water, I immediately filled it with WD turned it over, drained, repeated WD and then filled it with motor oil because that was what I had handy.
When I finally got a chance to take it apart, everything was OK.
