I used to have a fixed prop and got into the habit of leaving the transmission in reverse. It's part of my engine start up habit to snap the shifter vertical and give it a wiggle to make sure it's in neutral. My folding prop is not geared so it needs to be horizontal to make sure one blade doesn't flop down. There is a set screw on the coupling that is in line with the prop blades so I just make sure it's pointing up or down then I put the transmission in reverse to keep it there. I've been sailing with the transmission in reverse for 12 years with no signs of problems.