Tim, thats a great question and I would love to hear other responses to this. My criteria to this point is any spot where my dog could take a fall. The only trail so far, that I have turned around on with my dog, believe it or not is the Hi-Cannon trail. At the time we reached the ladder, it was early winter with a minimal snowpack and the ladders rungs were covered in ice as was the exit ledge at the top of the ladder. I left my dog at the bottem to "scout out" the ladder and deamed it to dangerous, a fall from either the ladder or the exit ledge would have been bad as there is a bad gully to the left of the ladder. We ran into the same conditions on the Willey ladders, but those are really steps, not rungs. On that climb I fixed my dog to me with webbing and we climbed the ladders together so he could not fall.The Great Gulf? he could do it, the Tri slides he has done, Huntington, nah thats not for us, he could climb the slab, but the class three above it, I wouldnt try. I will never put him in fall danger on any route.