It may not be a stray current problem at all. Your anode is "supposed"
to develop pock marks and become used up, and you would have much
greater cause to worry it were not.

I agree and if nothing else, it's either doing its job or indicating
that there is a problem. The dealer was amazed at the amount of
deterioration in such a short time so I feel it's excessive.

Tom, can you post a picture of the anode to show just how much it has
deteriorated since March?

Your definition of "deteriorating rapidly" may be what could be quite
normal, as Chuck pointed out.

The boat is in storage down at the bay but I'll try to remember to
take the camera next weekend. I was concerned and the dealer was
amazed at how fast it had eroded so I really think it's excessive
(although not excessive when you consider what it's protecting).

I would definitely trim the unit out of the water when the boat is docked as
that would be the best solution. Raising it is a one minute project (not
labor intensive other than to your thumb) and it will keep you lower unit
from looking newer.
Not a bad idea. Between the jack plate and tilt I can completely clear
the water.

As others have said it is also a good practice to turn the battery switch to
"off".
True but the dealer mounted the switch against the transom under a
hatch in the rear. When the bimini is down (which is most of the time)
I have to loosen the strap, move it forward, open the hatch and reach
down from a kneeling position to change the switch. A real pain but
worth it to save the boat I suppose.

If you have a stainless prop you may find a high rate of anode
deterioration. The stainless prop/ aluminum case/ zinc anode
are your source of current flow in brackish or salt water.

Raise the motor.
That is the case and could well be the problem. Also, the motor is
mounted to an Aluminum jack plate which is bolted to the transom. I
wonder if this could increase the problem? Anyway, it looks like I
need to raise the motor when at dock which is not really a problem -
just a habit I need to develop.

I want to thank everyone for the good advice. I'm leaving town later
today and won't check the board until the end of the week so if I
don't respond to a reply please don't think I'm ignoring you but I'll
catch up later. Thanks again. Take care.

Tom.............