I like the idea of the plexiglas cover over the panel for a number of reasons. If you have a put-together 'panel' like I have, you can add a protector just for the key. A piece of 2" PVC should do it. Glue this to the panel with the switch inside it. It doesn't necessarily have to be concentric, just so long as you can get two fingers in to turn the key.
Yes, it could probably be broken free of the panel when someone steps on it or kicks it; but it could easily be replaced and that would be warning enough for the skipper to read the riot act to that individual.
The sanest solution, of course, is to not have the keyswitch there at all. Fit a heavy-duty pushbutton switch like the Cole-Hersee M-626, with rubber boot, and leave the battery shut-off switch down below as your security. So long as the boat is kept locked (and the fuel and battery shut off) you're secure. (This is what I have on Diana.)
What? --you don't have a separate starting bank and separate shut-off switch for it? Tsk-tsk!
