Simple overvoltage protection
This type of circuit is often known as a crowbar. The diode is replaced with an SCR and the gate of the SCR is controlled by a 12.5V zener diode and a resistor. (resistor pulls the gate down to 0V and zener is connected from gate to 12V)

It combines the best features of both devices, the high voltage switching of the zener and the current handling and robustness of the SCR.