I've been wondering about this myself. The run has proven secure in the past. It belonged to my friend, whose flock grew to the point that this run was too small for them. Lucky me, because I inherited it! We're in Colorado Springs and have raccoons, foxes, hawks, the occasional roaming coyote, and on VERY rare occasions, a bear or a mountain lion (the last two almost never wander into town, but it's not unheard of, either). The run will be inside a fenced yard, and I do have dogs. The dogs aren't outside all the time, but just the fact that they are here seems to keep other animals from wanting to come into the yard. I think the most likely problem would be a raccoon, since they are common and can go right over the fence and into the yard. Nonetheless, when all is said and done, I'll probably lock the chicks in at night. I do worry that they'll overheat, but the summers aren't overly warm here on most days. The chicks aren't in the coop yet, but the time is fast approaching. There are so many things to think about!