What do you use in your duck pen to cover the ground? I am open to just about anything? Right now there's small/medium boulders and river rock around the pond (much of which the ducks kicked into the pond). The rest of the duck pen has become dirt/mud. It used to br grass and wild plants (weeds). I am open to adding more gravel, mulch or sand. I'd like to find a ground cover plant that will grow faster than they can eat it and weather the traffic. I doubt anything will survive their appetite though.