This is for running multiple rapids, or not using the motor for the rest of the a day. ...
Run the engine and disconnect the gas line so the engine burns through the gas in carb and internal lines ( I assume you have a two stroke with a separate fuel tank.)
Wrap the power head in a heavy duty trash bag. Then wrap whole motor/lower unit in one or two heavy duty black trash bags. Secure with duct tape. If you have two old Bills bags lying around (or other large dry bags, or even a tarp). Wrap the whole package in that and secure with straps. Strap the whole package on top of frame or amongst the gear pile horizontally, diagonal, angled what ever floats your boat.
Run clean conservative lines, you got the motor and gas dude.