A clearinghouse for shares held in margin accounts.
There are shady operators who enable share price wreckers.
"First, if you have over $100,000 at IB and do not have portfolio margin, you will have to sign up for it to access IB’s new stock borrowing system. Traders with under $100,000 in equity are not eligible for portfolio margin.
Interactive Brokers just unveiled access to the AQS stock loan marketplace. This allows short sellers to borrow shares directly from stock lenders at auctions that occur every 15 minutes throughout the trading day (from 6:45am until 2:45pm EST), bypassing the standard, opaque broker to broker share lending market. Short sellers can see exactly what interest rate they will pay for hard to borrow shares and once share are borrowed they can be shorted whenever, allowing the short seller with foresight to borrow shares in anticipation of selling them short later in the day or the next day. The shares remain borrowed until the short seller returns the shares or until the lender recalls the share. I am not sure whether the shares can be shorted, covered, and then re-shorted throughout the day"
The answer is simple, own your shares in a cash account.