We used t-posts too, but in the corners very large wooden posts, set deep. They came from small trees in our forest (about 4" diameter I would say). This provides a lot of stability. I also have bird netting over the top of open areas (between trees) to keep the eagles, hawks and owls out. We went with regular fencing, but I couldn't say which, similar to what Ghosty used. We've had the run 4 years and nothing has knocked any of it down. Good luck with your new run! I love when chickens have lots and lots of space to explore!!!