BTW Scott - I agree with those advocating rock molds and use them extensively myself.
Here's an option - the "rocks" shown below directly above the GG-1 were created with simple aluminum foil. First, you "steal" the foil from your wife, crumple it up, and then stretch it back to a reasonable shape, spay it with a wetting agent (plain water with a drop of dishwashing liquid), cover it with hyrocal from Woodland Scenics, apply it to the desired area, and then remover the foil before the hyrocal completely sets up.
