On the cooyotte we see the veines of the stone look fragil.
I never try to sculpt. But i think i will not have the hand the eye for it.
Do you ever try to use scupltris software. it is very different then with a modeleur. Start from a sphere and with some special sculting tool
we make a piece or a head .
There one free the name is sculptris i will post you the link.
I found the link
http://www.drpetter.se/