We test a few different methods for protecting yourself against an LRAD system. Nothing - 3:54 Earplugs - 4:50 Standard Headphones - 5:54 Electronic Headphon...
This video has some interesting points, maybe shields with the opposite curve might be the way to go.
Don't build a shield that curves away from you, but that's a useful trick to know for sure.
Also, don't build a shield that straps to your arm like these guys.