An apparatus and assembly for retaining a substantially flat, protective panel within a frame such as a window frame. In one embodiment, the panel retention apparatus of the present invention includes a bracket member for fitting over an edge of the panel, such that the bracket member provides edge and lateral support for the panel. The apparatus further includes a rack and gear mechanism affixed to the bracket member. The rack and gear mechanism preferably includes a circular driving gear and a rack member having a foot member attached at one end and further having a rack gear engaging the circular driving gear such that the rack member is linearly movable with respect to the bracket member responsive to rotational actuation of the circular driving gear. In a preferred embodiment, the rack and gear mechanism components are fabricated of a Delrin composite material which provides a lightweight, corrosion resistant, and low surface friction actuation assembly.