FWIW, on a day hike into Loch Leven Lakes above the Yuba Gap a few years ago I ran in to a guy on the way out whose Rottweiler had thrown in the towel and laid down on the trail, refusing to move any further. Apparently his paws just weren't used to the rocky trail. The dog had been sitting there for over an hour. I tried to pick him up but he growled and bared his teeth at each attempt. I eventually left him and reported it to the ranger station near the trailhead. The ranger didn't seem very sympathetic, who could blame him-he said this happens all too often every summer-and said that he would see if anyone was available for rescue. However, he said they didn't usually do anything.
I run my lab daily 1-2 miles on a gravel road to condition his paws and have never had a problem, even on hikes as long as 15-20 miles. You can't take a city dwelling pooch on a big hike and expect them to be trouble-free. It's common sense.