colored pencil on rocks! (looks like dichroic glass!) SBG thinks you can spray on waterproof sealer and spot them into strategic places in the garden or among potted succulents. Thomas since you love you some colored pencil. and garden.
Rock painting has become very popular these days. Pick up rocks and paint them in the pattern of cactus, arrange them together with some natural rocks as you like in a flower pot for a stunning homemade centerpiece!