Reading an animal rock painting book was how I first got inspired to paint rocks. I had painted on rocks before, but never thought of painting animals on them. It is a very satisfying medium to work with, as I have found out over time. For some reason, I paint well with acrylics on rocks, but I fail badly when it comes to painting on canvas.
A thin linear brush or detail brush that can be found at craft stores. Long, sweeping strokes with a linear brush create crisp lines; a detail brush helps with tiny fur strokes or a spark of white in the eye.