Actually, they rarely fall while I am in the process of making them. Exceptions being the rule, there have been specific pieces which have required a long period of focus, sometimes hours. The truth is that I focus on 'not allowing them to fall' resorting to begging the stones when necessary. Given my preferred size of stone, large or larger, I just couldn't continue if they fell.

Having said that all of my pieces fall at some point, many waiting years for that brief moment of freedom before settling into the dirt.