What you're talking about is a hedge. Hedges are expensive. A better strategy to a lot of investors is to "hedge" by trading smaller. Of course the spectacular

What you're talking about is a hedge. Hedges are expensive. A better strategy to a lot of investors is to "hedge" by trading smaller. Of course the spectacular failures you name were spectacular because they weren't hedged and were done with immense leverage. There is no way looking forward to predict if a hedge that eats 1/2 your returns every year is a better investment than just taking a catastrophic loss every several years. And it's not as simple as taking a 50% haircut on every trade: in reality maintaining a hedge will turn many of your small winners into losers. I personally guard against the prospect both by staying small (trading with only a small portion of my total account) and by maintaining net short deltas (beta-weighted). Keeping short deltas in a bull market with upward drift also has a cost, but it lets me sleep easier at night.