The S&P500 is one of the most widely held indices in the US. And yet, the Market Cap weighted version has a tendency to become dominated by a handful of big caps. This is especially likely towards the end of a major run, when a handful of megacaps dominate the trading action.
One possible solution? Replace, at least in part, the cap weighted index with an equal weight S&P: SPDR S&P 500 (SPY) with an equal weight ETF such as Rydex S&P 500 Equal Weight (RSP). See the Table below from The Chart Store: