I have been using an Exacto #2 knife for years and most of that time have been unhappy with their so called "safety cap" because it is just the opposite, falls off in your pocket or anywhere else it might decide.
Out of necessity I came up with a cover that is really safe. 3D printed and now FREE in the Repository Forum for anyone to download and print for themselves.
It also has flats built in so it won't be rolling around your work bench.