Nifty! The figures are the focus, so I wouldn't worry so much about background. I did think the white dragon was closer in the foreground, though. You may want to try a thin shadow under where the head rests on the rock, as you did at the front of the snout, and a slightly wider shadow where the rock falls away from under the neck. That shadow can be discontinuous from the shadow on the ground.
Rocks are very difficult for me - trying to get a given rock's texture right either requires more time and patience than I possess, or I'm just zapping out a cartoon and detailing would give the object more importance than it warrants.