Over the years of lending and never getting items back I have learned to ask for the item after a month or so. Usually I just say, I need it back to do something or someone else needs the item. (I usually blame it on my sister since she lives out of state, and I say I need to send it to her.) It wouldn't occur to me to ask for collateral - just say when you lend it you will need it back in a week or 2 because of whatever reason you want. Some people do forget, so it is not usually intentional just ask for the item back. If they say they already returned it ask them to be specific when it was, maybe you forgot they returned it.