As long as the business end (the "exposed wire" bit) is above the waterline and not hiding behind metal or carbon fiber or soaking wood, it will work fine. If it is reasonably out of sight, a blob of blue-tack is as good as anything to stop it flopping around.
Metal definitely deflects the signal, carbon fiber probably does, soaked wood probably absorbs the signal. Old, long aerials were only "sort of" tuned lengths, losing a bit of length by hiding it, nobody noticed. The inch length of the 2G4 sets is very much a tuned length, and shielding it loses all of the signal. But dry wood, resin, plasticard, all are transparent to radio signals. And don't worry about the metal railings, they will not be in the line of sight as far as the radio signal is concerned.