Being on an island with much free time on my hands at times, I spend some of the time designing a freediving noseclip that is fairly easy to make using readily available materials!  The latest version, while not the sleekiest, turned out to be quite comfortable.  Zero carbon footprint.  100% leftover bamboo!  With a little strip of used rubber to prevent slippage from the nose, it works great for static.  Waterproofed, it could perhaps be tested for depth training.

Disclaimer: This design is not a substitute for a proper commercial freediving noseclip.  This may not be suitable for depth training.  Do not attempt freediving without attending a formal freediving course.