Theodore Roosevelt national park - Armor Yourself!

Imagine that you fell from an embankment into a stream bed with just enough water to tumble you slowly along its course. Slowly you accumulate particles, small at first, then larger chunks as your body mass increases. In the end you would have a pretty good set of mud armor protecting your core. Your would be an armored mud ball; originally a chunk of rock that fell into a stream bed and came out with a layer of protective armor.