Not quite unspoofable, at least once the signal has been received for time-delayed rebroadcasting/meaconing. But spoofing does become detectable by any receive

Not quite unspoofable, at least once the signal has been received for time-delayed rebroadcasting/meaconing. But spoofing does become detectable by any receiver with a sufficiently accurate clock (I think for complete protection it would have to be an atomic clock though).