Cover for GPS worn on thigh

I like to wear my GPS rubber-banded to my thigh, so I can see it well and check it often,but it can take a beating there, but if the screen gets hit hard, the screen and GPS are toast, so I've been taping a piece of clear hard plastic I cut with a box cutter from a CD case over the screen, and it works pretty well.   I also made an extra long lanyard to tie to the bottom of my life jacket, and I can stuff it in a pocket when I'm not using it, or transporting it.  When I need to pull my rain pants down on the yak, I just slip the rubber bands down to my ankles.  Low-tech, but it works.   I  score the plastic with the knife and then break off.  I tried a fine hacksaw blade but it didn't work, maybe there's an easier way to cut the plastic.
   

Pictures, pictures, pictures!!! 

Sounds awesome but a picture is worth a thousand words. 

Try the stick on GPS screen protectors. Also good for fish finders.

Here's your answer:

http://www.overboardusa.com/waterproof-gps-psp-case.html

I'm assuming it is a WP unit.... You solution seems a good one! Lexan at home depot might be more durable to protect the screen. velcro sticky strips to mount it to the unit. Rubber bands are awesome!!!!

Picture now attached - my upper 1.2% age-bracket brain couldn't remember to attach the picture I took for the purpose!   
  The GPS is waterproof, but the screen is not knock-proof  - so the waterproof case with soft top is no help and unless the stick -on screen cover is some hard material, that won't either.    I'll have to check the Lexan out.  Thanks for your suggestions.  Keep them coming.