I think we Should do a craft day and Mass produce some of these Rubber Door Mats pressed into a concrete mold and later removed, to make stepping stones. There are lots of other smart concrete project ideas on this page.
Check out info on resin casting. You have a mold, mix the resin with a catalyst. Whatever is in the mold gets embedded in plastic. - This link doesn't include info, but it's a reminder to go check out more info on resin casting