A trench shoring or shielding unit, for securing the sidewalls of an earthen formation, trench or excavation, includes a plurality of adjustable, vertically arranged panels forming a protective wall. As a shielding unit, two opposing protective walls are spaced and attached by at least two spreader bars. Each adjustable panel has opposing top and bottom ends, a C-shaped channel traversing the panel's height, and opposing side edges that inter-engage with the side edges of adjacent panels. Further, each adjustable panel is attached to at least one of two or more whalers along an inner surface of the panel by a clamp-like fastener having a bolt passing through the whaler and into the C-shaped channel of the corresponding panel. The inter-engaging side edges are segmented, preferable concave and convex, so that adjacent adjustable panels inter-engage to resist lateral torque or twisting that may be caused by shifting or collapse of the excavation.