I am not bringing up the discussion on the frequent mix-up of these two, which I think has already been covered. Rather I am wondering whether anyone has devised/found a way to explain the difference between them to people who are not very knowledgeable in grammatical parlay, so that they will remember it (like a mnemonic device). My co-worker keeps getting them mixed up in printed public notices, though I have explained about possessives and verbs time and time again. He says he can't remember which is which and which is for what!

Any help out there?