An instrument includes components configured to secure a locking device inside a rod fixation assembly. In one embodiment, an instrument includes an outer sleeve and a pusher member arranged telescopically within the outer sleeve. A drive assembly cooperatively engages the pusher member. In another embodiment, an instrument includes an outer sleeve, a pusher member arranged telescopically within the outer sleeve, and a pair of drive assemblies. A first drive assembly engages the pusher member to distally advance the pusher member under a first loading. A second drive assembly also engages the pusher member to distally advance the pusher member under a second loading, the second loading being substantially greater than the first loading. In another embodiment, a method for reducing and locking a spinal rod includes the step of advancing a locking element while the locking element is retained in a fixed orientation.