During engine testing run-ups I discovered that I had lost one of the screws that holds on the canopy. I've heard that using Loctite on the screws that hold on the canopy will damage the canopy. However, I found the following "plastic safe" treadlocker, and tested it on a couple scrap pieces of the canopy for a couple days. I didn't see any damage to the scrap pieces, so I used it on all the screws on my canopy. So far, so good - Your mileage may vary.
Permatex 19920 Plastic Threadlocker, 10 ml
http://www.amazon.com/gp/product/B003ERTZWA/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1I had also tried two part epoxy on a couple screws. It seemed to work well too, but was messier, and the kind I had started hardening too quickly.