There's a way to short that no market can stop (sorry, Europe!), which I used in my experiment: sell your own holdings, and promise yourself to buy them back later. You are short the shares you sold, until you buy them back at a later date.
Something to keep in mind: If you don't use your own shares, but instead establish a "short position" at your brokerage, your risk is very different. If you sell $5,000 worth of stock short, and that stock goes up 5x, you now owe $25,000. You don't lose -100%, you lose -500% in that example. If that's news to you, learn more first.