Agree with all above. Brian, my first iteration was 1' length of copper pipe. It worked well, but corroded in hours and I didn't trust Cu oxide for contact, so changed to bronze. A short bronze rod or pipe might work if you can find one. Another idea worth trying would be to just trail a couple feet of tinned braid (short enough to not reach the prop in reverse!) . Interestingly, my tinned braid dropper is green where it is above the waterline, but still pretty un-corroded where it is under water when used.
What I am going to try this winter is to hook my braid from the nearby thru-hull through a relay to the tuner ground lug, then energize the relay with the switched 12V to the tuner. That way, when the radio/tuner are off, there is no DC galvanic path to the thru-hull. I think I like this better than the conventional blocking Capacitor coupling method. The thru-hull I use is on the centerline and less than a foot under water.
What I am going to try this winter is to hook my braid from the nearby thru-hull through a relay to the tuner ground lug, then energize the relay with the switched 12V to the tuner. That way, when the radio/tuner are off, there is no DC galvanic path to the thru-hull. I think I like this better than the conventional blocking Capacitor coupling method. The thru-hull I use is on the centerline and less than a foot under water.