Pour half of the Scotch into another bottle and hide it. Then top up the first bottle with a bodily fluid of roughly the same colour..... That stopped the cleaners thieving my whisky when I was a student....
Or maybe it was the ExLax in the Suchard chocolate wrapper?
At another place, there was a problem with frozen meals being pinched by those not entitled. So a small sign was made up:
"WARNING - If you wish to gamble, go ahead. You might be lucky and get a normal frozen meal. Or, less luckily, the one with added salt. Even less luckily still, the one with added laxative. But if you're
really unlucky, you might just get the one containing a deep frozen dog !!!!! I know which is which - do you? Feeling lucky, punk?"
Funnily enough, the thieving stopped! Even though, of course, we didn't doctor any of the meals!