Wash, clean, and dry all the rocks.
Paint rocks white to prime them. Once dry, then paint the rocks different shades of green.
While paint is drying, fill clay pots with the gravel.
Once rocks are dry, draw white dots, stripes, and designs on them with the paint markers to make them look like cactus.
Using the hot glue gun, glue flowers and/or googly eyes onto the painted rocks.
Once all the cacti are dried and decorated, arrange them in the clay pots. Push them down into the gravel a bit to keep them steady and standing upright.