One of things that students often struggle to understand is the ability of slopes that appear to be extraordinarily unstable to remain standing for long periods. Take for example this site, taken from this site:

You might (quite reasonably) ask how it is that some of the blocks on this slope can possibly remain in place through strong winds, heavy rain, snow, ice and rapid temperature changes. However, the combination of rock friction and interlocking between blocks can provide remarkable amounts of resistance to movement. Perhaps the best demonstration of this comes in the form of the rock balancing artwork produced by Bill Dan, who is an artist who specialises in this extraordinary work. Bill runs a blog (here) in which he features rock balancing from around the world. I think my favourite example to illustrate rock slope stability is this one, which can be found on a flicker site here:

I think I might run a student practical in the future to describe the ways that rock slopes work, based on the above image. Add it to this one (from here), and a huge amount about rockslopes becomes clear: