Actually, the data on a cd is inserted onto the foil between sheets of plastic by tiny monkeys, so it can't really "slide off"... but if you look closely you can see that the foil is still exposed all around the edge. I have tried sealing it with clear nail polish, airplane glue and sealing wax. Nothing really worked although with the glue I felt kinda weird for a while and the nail polish did have my fingers looking oh-so fab!
Damn poor engineering if you ask me!