Most of them say that. I always bring at least 2 boards on every trip. My method is I go extremely nuts on packing the boards. I mean I make it soo inconvienent for them to open that most times they just peek inside and thats it.
What I do..
1 board sock.
1 bubble wrap bag (homemade - big enough to fit 2 boards)
I slip both boards in the sock, then into the bubble wrap. Tape up. place into board bag. Then I spread towels out on them. Then I fasten the straps. zip the bag up then fasten the outer straps.
It might seem a bit much...but, I have never been caught using this method.
Thanks, COPA is good they only fly out of DC though. I'm going out of BWI. I've always brought a double bag, sometimes you might get dinged for two boards but I don't want to be at the airport and be told "one bag, one board or no fly".