The best ideas I have for painting a particular rock is met with the challenge of actually bringing the idea to fruition. Sometimes, I just like to take a drawing from the past, scan it, bring it into an image editing program like Afinity™ and shrink it to the size of a rock and then print it out on Sticky-back gloss paper. This produces a tightly rendered pen and ink replica of the original that will fit nicely on a flat rock.
Lastly, the rock gets adorned with the usual glitter and glow paint that is typical of most of the rock creations. Below is an image that was drawn about a year ago. The original is about 9x12" and is of a fire breathing dragon.