My son has been playing Guitar for a year and loves it. We have been through half a dozen pic holders made of cheap rubber. He also loves survival bracelets. It would probably be best if I had flexible filament, but I do not. When the paracord is threaded through the back it acts as a spring to keep the pic in place.
The clasp is http://www.thingiverse.com/thing:96174. I increased the size and drilled out two of the holes to fit the paracord.
Print upside down with support. The slot for the pic will need to be cleaned up .
The bracelet itself is rather stiff. This is compounded by the fact that my son wanted to integrate his watch into the design. I would suggest removing the core of the paracord if you plan on adding a watch.
Then again I could just be tightening the knots too much.