Pickle Juice Ploy

A friend of mine has her 40 something son living in the upstairs of her house,it is pretty much like a self contained apartment with cooking facilities and bathroom,but the son still enjoys sneaking down and "borrowing" food and pretty much anything else that isn't nailed down on a regular basis. She mentioned to me the other day that she was pretty sure he had gotten into her vodka and was wondering how to catch him at it. I immediately stepped up to the plate to offer my assistance. She had thought of watering down the vodka and I said,no don't do that,no need to ruin perfectly good vodka,instead wait until you have an empty bottle and fill it part way with white vinegar. She said she didn't have any white vinegar on hand but would use pickle juice instead. I visited with her again today and inquired about the pickle juice ploy,she said she chickened out because she was afraid he would choke on it! I pointed out that if he didn't choke on straight vodka I wouldn't worry to much about pickle juice and she admitted that she was afraid of what he might do as a pay back if he had fallen for the pickle juice trick,so it's back to the drawing board for me!