[Joseph Smith]

What are you using to retract your winch? If you use the right gearbox/motor combination, it won't backdrive at all. For example, our winch was originally retracted by a BAG motor in a 100:1 planetary gearbox, and when the motor was unpowered, it backdrove extremely slowly (we used a talon SR to control the motor so it automatically applied brakes when it wasn't powered). At this point all it took was to program the motor to servo to a specific position and it would hold it there without any other mechanical lock. The BAG motor was capable of holding this position for several minutes and barely even got warm. Recently we switched to a 50:1 planetary, which backdrives faster and requires more power to hold, but the BAG still holds the position fine for us. We use an encoder on the winch shaft to keep track of our loaded position and a VEX ballshifter to shift from engaged to neutral, so we just hold the winch in place then disengage the shifter to fire. This also allows us to vary our shot power, because we can just change the winch position target and the motor will hold it there.
There are other options, too- some gearboxes fight backdriving by design, such as a worm-drive similar to the window motor gearboxes. However, all of these ideas hinge on whatever method you use to fire.