How can he get his co-worker(s) to stop stealing his stuff?

How can he get his co-worker(s) to stop stealing his stuff?

“I like to drink seltzers at work so I keep a bunch of them in the breakroom fridge. I noticed some would go missing, so I left a ‘please don’t touch’ note in the fridge but they continued to go missing. I haven’t been able to figure out who’s doing it.”