A locking clamp for use in a cable system for stretching a sheet across a surface and maintaining it under tension, the locking clamp having a base member defining a first grasping surface; an elongate tongue member rotatively coupled to a first portion of the base member and defining a second grasping surface, and a locking member that is rotatively coupled to a second portion of the base member and that is configured to selectively rotate the tongue member to urge at least a portion of the second grasping surface of the tongue member into engageable contact with the first grasping surface of the base member. The base member of the locking clamp also has a hook configured to removably engage a cable of a tensioning system.