Sorry about the holes, but tiny pad eye on mast, invisible
fish line to
shroud, secured with a double running hitch would get rid of cormorants and shags,....so who are befouling your
boat?
The height above the spreader needs to be suited to whoever you wish to dissuade.
The dead bird trick does seem to
work, but, yuck! Just make sure the bird lice have left first. Or, some friends reported success with a feather duster aloft..... "Oh, poor uncle george!" But they did say it works. Never tried it, mostly we move on before we become a target.
Ann