Prevent a detachable hood from unzipping

I recently did this small mod on one of my jackets that I thought you might like: it's a waterproof hunting jacket with a detachable hood. The problem out here is that the rain can be on-and-off all day long, leading you to put the hood on and off a number of times, without ever actually taking the jacket off. Anyway after a while, I encountered a slight design defect: every time I would through the hood back, the zipper would slowly but surely open up, until it was halfway open. The fix seemed pretty simple: put a hook on the end of the zipper and attach it to something on the jacket. The problem however was that there was nothing on the jacket to attach the hook to, and I didn't want to sow through the jacket, in order to not damage the waterproof lining. So after a couple of ideas I didn't like, I finally thought: sugru!