[[[[[.......potential daytime predators are hawks and eagles, neighborhood dogs, and feral cats (unlikely, but possible). ......]]]]]
With loose neighborhood dogs, your ducks will never be safe outdoors unattended, not at any age, unless that electric fence is at least 5 feet tall. Dogs will simply jump over a low electric fence and they love to kill squawking flapping ducks.
Hawks and eagles, perhaps. It takes a very large hawk to attempt an adult duck; most hawks won't. They will take ducklings, though. Eagles are capable of killing ducks, but domestic ducks on pasture don't seem to meet their criteria for hunting. They seem to want to take them out of the air or off of water. It would be bad luck, indeed, to have an eagle interested in your ducks. But it can happen.
Add crows to your list of potential duckling killers. They are certainly capable of killing and eating half grown ducklings.