Make a Stepper motor Hold/Lock

I have a stepper motor and i need it to lock/hold in place how do i go about doing this? :~

Well, you could just keep those particular poles energized, but that would either drain your battery or burn out your stepper motor (if the voltage is too high to begin with).
Another thing you could do is make some kind of disk break, similar to the ones used on hobby RC cars/trucks.

Here is an animated explanation of how steppers work;

Here is a good diagramatic explanation;
http://www.solarbotics.net/library/pdflib/pdf/motorbas.pdf

At rest a stepper motor will have full torque - as long as the coils are energised. Providing the motor is appropriately sized and you can provide it with power then the motor will be locked in position without the need for a separate brake.