Having lost some Koi to herons in previous years I had fitted several types of ugly netting over the pond thus spoiling my view of the fish which for me are therapeutic to watch on a balmy summer evening - well almost any time of the year really. Then I saw the advertisement for Netfloat rings and decided to give them a try. I live in The Netherlands, my kidney shaped pond is 8 metres long and 2-2.5 metres wide, in an open garden regularly visited by hungry herons. I had to arrange for the rings to be sent to a friend in the UK and I picked them up by car some some 4 months later. They were relatively easy to fit but needed 'shaping' to the contours of the pond and, because I have 2 inlet jets coming into the pond keeping the water circulating, I had to tether the rings to the side of the pond at places where they tended to float into the middle. Since then there have been no losses of fish despite the fact that I have seen herons flying over on several occasions.
I cannot say 100% that the rings have prevented the herons from taking any fish, but this is the longest that I have gone without losing any, so to me they appear to be an effective deterrent. Not only that they look quite neat despite the fact that I have no plants in the pond only around it.
They do collect alga, and although this is easy to remove with a garden hose getting the rings out so as not to disturb the Koi is a bit of a hassle - hopefully future rings will be impregnated with something that stops the alga from growing on them but for the moment it is not a real problem.
Overall I am very happy with the product.
PS it would be impossible for a heron to walk on the rings without sinking so I do not understand the comment of Mr James.Netfloat Ring - the pond protection system