Combination of theft proof screws:

https://www.brycefastener.com/?keyword=tamperproof&gclid=EAIaIQobChMIzauLx_ar5wIVWyCtBh1TXQwwEAAYASAAEgK-E_D_BwE

and locktite

https://www.amazon.com/Loctite-Threadlocker-Red-0-20-209741/dp/B000FP8EUS/ref=sr_1_1?keywords=loctite+red&qid=1580408067&s=hi&sr=1-1

Combination of theft proof screws.

These are screws which can only be removed with a special tool. There are so many different kinds that it's impractical for a thief to have all of these.

https://www.brycefastener.com/?keyword=tamperproof&gclid=EAIaIQobChMIzauLx_ar5wIVWyCtBh1TXQwwEAAYASAAEgK-E_D_BwE

And Locktite (or an epoxy). This is an inexpensive adhesive which makes it more difficult to turn the screw.

https://www.amazon.com/Loctite-Threadlocker-Red-0-20-209741/dp/B000FP8EUS/ref=sr_1_1?keywords=loctite+red&qid=1580408067&s=hi&sr=1-1