Well, I'm not sure if I've stretched them out or what but my black pair, which I have worn often (but are only about 9 months old), are constantly slipping off my heel. I'm seriously ready to get rid of them because it's getting annoying. Anyone else experience this after wearing them for a while? I'm not wearing them with socks or hose, so they're not slipping off for that reason. Anyone else having heel slippage?