Katabatic, thanks, but I'll carry my spare on the back deck. There is virtually no way my spare could go adrift unless the very stout bungies break. It would be very awkward on the front.
One thing I've learned about myself from trying different paddles and modes and that is to do everything in moderation. Maybe especially when powering up with a high angle. I seldom go all out anymore and I haven't had any shoulder, or any other issues for a long time. I'm even back to doing full pushups and other exercises that I couldn't do for a couple of years, because of stains and pains.