Cool work Bob.
I wonder what happened to the stones? That clipfile is pretty old and I'm pretty sure I would make it totally different now, technically.
It may not work properly anymore. If you wish I can take a look at it.
I agree that the background is perhaps the strongest feature in this image. It looks VERY realistic!
I like the sand though, it's very smooth. You could try adding 0.0025m stones in different grain colours to simulate sand.
(beware that the suggestion of 0.0025m stones is based on the assumption that you're using real world scales)
Cheers,
Martin