plants for ducks

Hi! Im looking into getting some wild duck species in the future, white faced whistling specifically but other species as well, and I was wondering about the construction of a pen for them. For one, how big it should be, two, what materials to use and how to properly protect it from predators...

I have five, four, and three week old ducklings and I finally got the duck house built in the section of the yard that I designated for the duckpen, but I need some landscap--I mean DUCKscaping advice! The duck-pen area was a part of the yard that hasn't been used for anything for a while and...