re: s&P etf to short the market

From 2/25 Economist Article:

Valuations are reaching sky high levels. The most closely followed measure of them was devised by Robert Shiller of Yale University. It compares prices with inflation-adjusted earnings over the previous decade—a long enough period to smooth out the economic cycle. The resulting cyclically-adjusted price-to-earnings ratio, or cape, has never been higher than 44.2, a record reached in 1999, during the dotcom bubble. The previous peak was in 1929, when the cape hit 31.5. It now stands at 34.3.

thinking about a small'ish combination long / short portfolio position for next 12 to 18 months.