I've been tumbling rocks with my kids for about a year now. Two tips that made it actually sustainable: (1) ceramic media is a must-have, not optional - cuts the noise by 80% and you can run it indoors, and (2) skip the "perfect rocks" hunt and just tumble broken glass bottles instead. Takes 2-3 weeks vs 2-3 months, looks amazing, and my kids can actually see results before they lose interest. We keep a jar of the sea glass pieces on the kitchen counter and it's become a surprisingly nice conversation starter when guests visit.