hey,
first thing i did was i bought 5 sheets of polyurathane (foam) from home depot for 5 bucks. cut a square of foam and stuck a rocks on it, cut groves, etc. then I bought pre-mixed tile adhesive (grey) and I spread it all over the rock wall, this gives it the hard feel and protects it. then I took polly acrylic finish and put it all over the rock wall with a brush. took sand and layed it on top.
thanks,
Craig Condon