To make a river stone mat first you have to gather or purchase river stones. After that take a plastic mat and arrange all the stones on it. Then stick all the stones one by one to the plastic mat by using silicone sealer. Let the sealer dry completely.
FINALLY - a use for all of those toilet paper rolls that Dave keeps. Recycle Toilet Paper Rolls For Organizing DIY if you are in a financial pinch or just want to be crafty. perhaps wrap in some stiff paper for more support