Re: protecting the upper half of the rudder shaft. Our fix is to use half of a battery jump cable with one end clamp removed and replaced with an anode. Clamp the cable to the top of the rudder shaft under the tiller head fitting and drop the anode end overboard. Been doing this for 30 years and have needed to replace a bunch of anodes (and a few jump cables), but no upper rudder shaft corrosion. No zincs on wood problems.