They might move to the lower pond now that the upper is netted. Keep a good watch. I battled the heron for 2 plus years , daily visits, multiple visits every day. The floating alligator heads, made them move slower, stalk slower, but they still fished. The fishing line, they learned how to dive over, through, etc. I had it strung tight 6 inches apart.
Chicken wire fence, jumped over and floated in the pond stabbing at the fish.
Had a floating island, they used it as a sushi bar, island gone.
Finally netted with the wide weave net, high over the pond, that stopped the suckers. They must be able to see it from the sky since they still fly over almost every day, pause in the air and keep going. We had one land this year, but our barking yorkie scared it off, it never came back.
I like the wide weave around 2-3 feet over the water, I can work on the pond, no little birds, dragon flies, frogs etc get stuck. The plants can grow without running in to a net. And it is not that eye obtrusive.