In article , angel toledo
wrote:

Christmas time is coming up and I'm alread thinking about creating some
sculptures to fill my front lawn. My plan is to create a wooden frame
onto which I can model my masterpiece. There's only one problem: I've
never done anything even remotely similar to this. My first thought is
modeling clay, but I don't know how it will hold out in the rain.
Plaster? Again, I don't know what the rain will do to it. Cement? Too
heavy. If anyone has any idea that can help me out I would certainly
appreciate it. Any direction to a website or other group would also be
helpful.

"hypertufa" over a wire mesh on a frame, perhaps?

http://en.wikipedia.org/wiki/Hypertufa

--
Life. Nature's way of keeping meat fresh. -- Dr. Who