NEW YORK ( ETF Expert) -- There are times when the broader U.S. market moves sideways. In the last five trading sessions, in spite of rally hype, U.S. stocks have essentially parked the S&P 500 bus in neutral.In times like these, I often revisit all of my client holdings. Are there any underperformers that have not provided much in the way of diversification or income generation? On the flip side, do I own any assets that have dramatically exceeded respective price targets, where recognizing gains would raise cash for future buying opportunities? Raising cash is a critical component of successful investing. I may look to prune portfolios so that there is 10%, 15% or 20% available for an inevitable pullback in prices. (Believe me, there are enough August-September headwinds to hamper a five-week rally's upward progression.) Circumstances may dictate whether I buy the proverbial dip or wait for a technical bounce off a key trendline (e.g., 50-day moving average, 200-day moving average, etc.). Regardless, I am always evaluating prospects for my "wish list." One exchange-traded tracker that merits serious consideration on a selloff is Market Vectors Retail ( RTH). In particular, it has demonstrated remarkable resilience in spite of ongoing economic uncertainty. Give credit to RTH's 10% weight in Wal-Mart Stores ( WMT). Granted, some might regard a 10% weighting in any company as excessive. However, Wal-Mart has been nearly bullet-proof in both recessionary and expansionary environments. That fact has helped propel RTH to new price heights in August, Moreover, RTH has served up far greater relative strength than the broader S&P 500 over the last 12 months.