Custard Shoes

When walking up a shallow stream or river, it's hard to keep your balance not just because of the slippery rocks, but also because each footstep brings an exciting unknown landing surface, such as a sharp rock jutting out of sand, smooth rocks around a jagged twig, etc. Combine the thixotropic properties of custard, plus a non-rip covering and voilà! A shoe that solidifies with sudden impact, but is soft and pliable (and comfy!) when walking on gentler surfaces.