Try posting at gardening with rocks.

go to the hyperfurfa forum. I make molds using 4 pieces of wood, any size for the sides, and plastic on the bottom which then folds over the wood. it you want a fancy design, put a leaf on the bottom, rocks, etc-- before you put in the concrete. make handprints on the top, spell words, etc. if you want the design all the same, use a piece of wood the size with a design (wood nailed onto it, use caulk, etc and press it into the top of the concrete.