Thanks, I've seen other koi keepers do the same, my pond is natural so I prefer to use the natural cover, a neighbour has fake owls on their shed & I think they're close enough to deter the herron as it's not been back (to my knowledge).
My Dad lives in the middle of nowhere & has had a pond for a over 20 years where several species have raided it of simply fallen in... otters, herron, cats, dogs & donkeys to name a few.
Dunno what size bird of prey he'd need to deter a donkey.