I've been to a couple of Ozzfests. Pat downs are thorough. They check insides of hats, pat down to socks and even checked the small of my back for anything. I have yet to tape an Ozzfest show but I've got in a couple of shows now with a MD down pants so I might take more chances in the future at the heavier concerts.
I hate taping in day light outdoors. Be careful. Assume somebody is always watching, even other fans.