RFID isn't what you need, that's short-range stuff.
you should try looking into tracking transmitters... like you see on those nature shows where they track animals with the special collars on... basically you attach a small radio transmitter to the board and then you use a reciever with a directional antenna... that way when the reciever is pointing toward the transmitter, you get a stronger signal than when it's not pointing at it, so you can tell what direction to go to find it...
if you do a search for "tracking transmitter" you can easily turn up a transmitter circuit like this one:
**broken link removed**
(of course, you'd have to run that one at higher power or find a better circuit to get a more usable range out of it)
as for the receiver, well I am no radio guru so I'll let others chime in on that one...