I will say I bet there are owls and hawks in your area. They will dive bomb the pond. I had a large owl do it. I get bamboo steaks and string high test fishing line in a perimeter above the pond then back and forth a couple of feet above the pond so that there are no spaces for them to dive bomb. The perimeter is for the herons. I really hate the way nets make the pond look. I really think it ruins the enjoyment of a pond. When I have people over they don't even notice that the fishing line is there for the first few minutes.