If you keep them in their pen it will become mud fairly quickly. I'm about to make another one so I can rest the first for a year in the hope the grass will regrow. I use one metre wire pig wire so they can get their heads through to eat the grass on the other side, but if they are only in it at night then chicken wire will be fine. My ducks don't have their wings clipped but they are not flyers. I have a Swedish Blue drake, a khaki Campbell duck, and their three daughters. Not breeds known to fly.