If you're a stage electrician concerned about safety, you've probably more than once used a self-jammer to haul fixtures and cable up into the cats and balconies. Petzl Climbing Gear's Pro Traxion self-jamming pulley is perfect for this task, and is a chosen method for people across the industry. It's not cheap – Amazon has it for about $110 USD. It is completely worth it, however, for your working tool bag. When you let go of the rope, it jams closed and holds the load until you prove that you can take it again.