I did this during a break from some living room clean-up efforts (Note compressor hose in background).
And, yes, I agree that the top stone should be standing upright rather than setting so easily on that other stone's flat. So, after I took these, I fixed it that way.
Of course, shortly after I took these pics, I managed to knock the stack down with said hose. So, I relocated the hose and tried again...
Now, whether or not you were impressed with my truly humble attempts, you need to check these links to see how the pros do it. Beware, these are picture intenstive websites, but oh so worth it.
I am in awe. The next time I go to the mountains, where I got these few rocks, I'm coming back with a car LOAD!