Clear vinyl about .35 mm in thickness can be found at Wal Mart or
probably some fabric stores.  The stuff I found at WM is called
"Transsparente Vinyl Brillante"  I comes in about 52 inch rolls of
different thicknesses.  The thickest is about .35 mm.  Cost: $3.00 per
yard.  A half yard will do countless guitars.  Cut a piece and stick it
on.  Mark it with a pen the outline you like and cut it out.  Remove it
to clean your guitar.  This will NOT hurt the finish on your CA guitar. 
NEVER EVER PUT IT ON NITRO FINISHES.  IT WILL DAMAGE NITRO
FINISHES TO NO END AND FAST.  I WOULD NOT PUT IT ON YOUR
MARTIN.  A TAYLOR MAYBE.  BUT DO NOT LEAVE IT ON IN THE CASE WHEN YOU
ARE DONE PLAYING FOR SAFETY ON ANY WOOD GUITAR.

Some time ago I paid $10 for two Martin
size pick guards of this stuff on eBay.  Now you can cut your pickguard
to any size and shape you like to cover your pick scratching area.

Other uses: iphone, ipod, ipad screen cover.

Soundhole cover for feedback control.  Use a CD for a templete and cut vinyl circle and stick it on.  It works!