Methods and devices for locking a fastener in a thru-bore are provided herein. In one exemplary embodiment, a spinal anchor is provided that includes a bone engaging fastener, an anti-backout mechanism, and a locking mechanism. The anti-backout mechanism can be movable between a retracted position in which it is disposed within the fastener and a deployed position in which is extends from the bone engaging fastener. The locking mechanism can be matable to the bone engaging fastener and can be configured to move the anti-backout mechanism from the retracted position to the deployed position. In the deployed position, the anti-backout mechanism can prevent the bone engaging fastener from backing out of a thru-bore in a spinal plate.