If you organize your mechanical arrangements so that when locked the lock pin can't exert any torque on the servo arm then there is no need to have power on the servo.
One way would be to ensure that in the locked position the lock pin. the servo arm and the servo spindle are all in a straight line.
A better way would be for the servo to go a little past that centre position to a fixed abutment. Then all the force from the lock pin would be taken by the abutment.
...R