eck Fitz, that's a great trick you've taught him.
Dry stone with dog:
http://www.themodernantiquarian.com/post/43661
Wet Stone
http://www.themodernantiquarian.com/post/43659
I'll have to get one, it'll save me having to carry that humungous water spray about. You'd need a few Great Danes for Roughting Linn though ;-)