Bone (e.g., spinal) fixation assemblies are provided that resist back out of associated bone anchors (e.g., screws). The bone fixation plate may house a bone anchor retaining member that permits partial passage of the bone anchor and subsequently resists back out of the bone anchor from the member and the bone fixation plate. In some embodiments, the bone fixation plate may include an attachable cover member that prevents the bone anchor retaining member from ejecting from the plate. In other embodiments, ejection of the anchor retaining member from the bone fixation plate may be prevented by walls integral to the plate.