your best bet is a locked servo, because as I said before, a stepper motor rotates continuously when power is applied.
It does not. A stepper motor steps when it is told to step. It steps exactly once. The stepper driver needs to set the state of 4 pins right to make that happen. The exact state of the pins to produce a step depends on which set of coils is powered currently. That is why the control of a stepper is generally offloaded to a stepper motor controller. Well, that and the high current/high voltage needs of a stepper motor. Tell the controller to step, and it steps. Once.