The bait store down from my home often alligator turtles brought to them. I asked after a shell (which cannot be sold, but they will trade for tomato, beans and squash from my garden when it comes in). Can a banjo be made from a shell?
There was some sort of shell instrument in Walt Disney's 20k leagues under the sea. :-)
Seriously, practically anything can be used for the body, as long as it can take the tension of the head. If you are worried about that, maybe place a normal pot inside the shell, and just use shell as outer decoration? Or use a inserted pot/framework to stiffen the shell?
Hope you can make one, I'd love to see it, being a turtle guy.
Bill Rogers (Moderator)
'Banjo cake' 2 hrs
'Gold Tone BG-250' 2 hrs
'A song for Koriander' 3 hrs