I was thinking about it so I think it can be a good trade. But yes, that thing can get over 100, not sure for the 500 though. So you want to have a LARGE stop. What I would do is not placing a stop but hedge the position with OTM put options (on ES or SPY, or calls on VIX if there are any) to make sure I am 100% hedged over 100. This would protect you in case there is a 20-25% drop on the S&P, which is not impossible IMO, not likely but you want to protect your capital.