Maybe next time he wants to borrow something have him pay you a deposit
and tell him when he returns the item he'll get his deposit back. ;)
Make sure the deposit is more than enough to replace the item and extra for the hassle of getting it replaced in case it doesn't come home.
I'm kind of lucky mine don't borrow stuff they leave stuff instead,
so I end up carrying it around and moving it from one storage area
to another until I either wait til they show up and hand it to them and tell
'm to take it home or I get rid of it.