BALTIMORE ( Stockpickr) -- A rising tide lifts all ships -- except the ones with holes in the hull. They still sink regardless. >>5 Big Trades for a September Bounce That's why it's so important to stay vigilant in a bull market. Plenty of damaged stocks can appear to get lifted by a buoyant market, only to put your portfolio underwater when Wall Street catches onto the holes. Sure, a weakening stock can get floated higher temporarily by indiscriminate buyers in a bull market, but that doesn't carry over when the bears come out. When the broad market's in a downtrend, deteriorating firms are all but guaranteed to get sold off hard. The challenge, then, is to know what to look for before your shares get shellacked. So today, we'll attempt to spot the red flags in four big names. >>5 Big Short-Squeeze Stocks Ready to Pop We're looking at a combination of highfalutin metrics that point to money problems for companies. To make our list, a stock has to has to meet three out of these four red flag criteria: a bankruptcy prediction formula called Altman's Z-Score that registers at less than 1.8, indicating financial distress; rising CDS spreads, indicating that institutional investors are pricing in a higher probability of bond default; and dropping sales and inventory turnover. That quantitative approach to finding out red flags avoids the bullish bias that's historically put blinders on investors. So, without further ado, here's a look at four red-flag names to sell this fall.