Rick on Twitter: "Quick #electronics tip: You can use a p-channel mosfet and a resistor to add reverse polarity protection to a circuit if a diode doesn't work due to it's voltage
AN013 - Reverse Polarity Protection
Protecting Automotive Motor Drive Systems from Reverse Polarity Conditions (Rev. A)
N Channel Mosfet Reverse Voltage Protection - General Electronics - Arduino Forum
Over Voltage and Reverse Voltage Protection Circuit