I assume you mean so others cannot borrow your stocks to short? From what I read, it is largely a myth that listing your owned shares will prevent them being loaned out by your broker. However, the brokers can only lend shares that are held in margin accounts. If you have them in cash/IRA accounts (as I do), they're automaticaly locked up. Here's the source: http://beta.fool.com/beatlesforever/2012/06/04/shortlending/5274/?ticker=ARNA&source=eogyholnk0000001