4Amps current sensor circuit with lm358
You can use a hall effect current sensor (example) to detect the motor current. This device outputs a voltage proportional to the current it is sensing. Run this voltage into a comparator or ADC. The output of the comparator can drive a logic level FET that can cut off the voltage to your motor when it stalls. You will need to think about how you want the motor to come back on after a stall.

You could also sense current with a small shunt resistor in series with the motor in place of the hall effect sensor.