You can overdrive the axial ax10 - it has a front and read diff and they offer difference gear ratios. Perhaps you're thinking of dig where you can run the front/rear axle at different speeds to keep from having the back push the front too much on a very steep incline (it may offer other advantages but that's teh gist i get from dig)

your description of clamping it to the rocks makes perfect sense. best explanation I've seen yet.