Abstract: A cover (1) for temporarily covering a trench, e.g. in a thoroughfare such as a road or footpath, by extending over, and resting on the ground on opposite sides respectively of the trench, the cover (1) being releasably engageable with other adjacent covers (1a and 1b) by means of male members (5 and 5b) mating with respective corresponding female members (6a and 6) in such a manner that when the covers (1, 1a and 1b) are engaged in a ground resting position to form an assembly (7) of covers, one cover (1b) of the assembly can be disengaged from the adjacent cover (1) only by moving the cover (1b) out of the general plane of the assembly.