Netting only works well on small ponds as it stretches so easily. We put netting over our pond (a similar size to yours), which needed support in the centre as it sagged into the water. It did not work as the heron just walked across it! Once the hebes grew large enough it stopped the heron coming by. Kingfishers dive straight down so make sure there are no jutting branches overhanging the pond from which they can dive. Herons wade in to grab the fish and I don't think they like to get their feathers wet so plant heavily around the pond so there is nowhere they can stand and jab fish from the edges. Making sure edging wobbles stops predators like cats from getting too close too as they dislike unstable footing. I would suggest a wee wire fence, about 30cm high around the edge of the pond, might help more than netting. Another possibility is to cover the pond with one of those freestanding gazebo or portable carports you can buy these days.