That pen looks neat. I have most of my birds in 2x4 welded wire running along steel t-posts, with nylon netting as the canopy. They arent the most excuisite of pens, but they are easy, and very large. I've never had any pheasant dig out of my pens, the worst for digging are my eared pheasants, and impeyans. To keep predators out, I have electric wire run around the bottom and the top of the pens, and nothing ever gets in. you could lay wire on the ground around the inside peremeter to keep them from digging holes under if your concerned about it, but I wouldnt worry about it personally, as long as predators cant get in.