Any suggestions on plantings (particularly perennial) I can use to provide some natural cover/diversity in my run? It's basically 16 x 28 x 6 ft tall and I would like to provide the kids with some plantings for additional shade and interest. There are deciduous trees on the north and south sides of the run but I'd still like them to have some cover inside.... I'm in Zone 7; anything that will (probably) withstand digging and scratching without growing through the roof of the pen would be great. Thanks- Leigh