As an example, you sell an OTM put on S&P and buy an even-further-OTM call on VIX. VIX is a proxy for markets decline, but it's an imperfect hedge - you can imagine a scenario where S&P is down a lot while VIX has not reached your strike or something like that.
Unless you adjust in the ratios of how much of the put you sell vs. the amount of calls you buy then you might get close to a decent hedge.
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