The key to using a \"pony\" clamp is a brace across the doorway. because the pony clamp doesn\'t have a big lip it will pop off when tightened. The brace across the doorway prevents that from happening. Cut the brace to the exact size, you don\'t want to widen the doorway by forcing an oversize brace in there. You just want to keep the pony clamp from popping off.