I run a PA at random locations. My trick is using different heads. I use a phillips, a #2 square, an old school flat blade and a security torx. This makes removing the gear a much more difficult and time consuming task. Rack screws on 19 music racks is usually #10 x 32. You may find #12 x 24 or even metric M6 screws. Once you know what size you can get screws of all different sorts.

And of course, the best security is to never turn your back on your gear, ever.

Does what it's supposed to, but awfully expensive. Go elsewhere and buy an entire Torx security set for $7.95.