Ask around if there are any weasel or minks. When there's only a few, people may think they aren't around. So, seek out and confirm with multiple sources. A young mink or weasel can squeeze thru a hole as small as a quarter, an adult would slide right thru present fencing. When they kill, they get excited and often take out every bird within. The chain link fencing is really strong and can be the basis to hang 1/2" hardware clothe (metal fencing). I like that it reaches the ground. If you look over the perimeter daily, you could go with laying 24" of hardware clothe outside and attached to the perimeter chain link to prevent digging under. It doesn't have to all be done in a week. Yet if put off there you'll likely have a predator attack.
Those 2 will keep you company and provide moral support as you predator proof their pen. Later they'll show their gratitude for a long duck run. Nice pool, enjoy your life enriched by duckies.