On the same note with share borrowing, you have nothing to worry about if you have a cash account. The only way your brokerage can allow YOUR shares to be borrowed is if you have a MARGIN account. If you DO have a MARGIN account you can do exactly what Er0ck stated and call your brokerage to have shares of a specific stock excluded from being borrowed. You can also have your whole portfolio blocked from being borrowed against. Always call your broker and ask them