On Mar. 15, 2011, units of Enterprise Products Partners LP (NYSE: EPD) had a truly jaw-dropping trading day. The opening quote was $40.19 and proceeded to plunge as low as $27.85 intraday before closing at $40.20. Since then, they’ve traded back up over $42, squarely in the $40 to $45 range held since last autumn.

Our first reaction on seeing this kind of action is that there’s been a bad trade. In other words, the unit price never went that low in reality; rather, the low levels hit were due to electronic error.

In this case, however, Enterprise really did trade at those levels, i.e. orders were actually filled. Mar. 15 marked the bottom of a two-week downtrend in the unit price, which began shortly after the MLP announced a merger with affiliated Duncan Energy Partners LP (NYSE: DEP).

That deal was met with mostly positive feedback on Wall Street, which now has 19 “buy” ratings for Enterprise against just two “holds” and one “sell.” Predictably, there were also the requisite unitholder lawsuits, aiming at squeezing out a higher bid price. And the move also seemed to arouse fear among some investors about possible dilution.

Ironically, the dramatic events on Mar. 15 had no visible catalyst and occurred following two modest up days for Enterprise units. Within minutes of the open, a huge volume of “sell” orders came on the market, overwhelming “buy” orders temporarily. But by 10 am the units were already on the mend. In fact most of the trades that day did go off between $38 and $40 per unit.

In short, unless you were paying close attention on Mar. 15 you probably didn’t notice anything at all. But there were definitely some big-time winners and losers in Enterprise units that day. In the latter camp were all those who were “protecting” themselves by using stop-losses. We’ve warned investors time and again not to use stops on any position they’re holding for yield and long-term wealth building.

The primary reason is that stops have become very popular for investors who are worried about another 2008-09 decline but are loath to take profits on winning positions.

Particularly popular are trailing stops, which adjust upward along with the price of a stock.

If enough stops are in place around the same price, breaching that level will execute a huge number of sells at the same time. These “sell” orders will overwhelm the bids, sending the stock in question cascading lower. Stops will be taken out at the first available price, which is usually well below the actual stop price set.

In the case of Enterprise on Mar. 15, the losses were quickly erased, as the units quickly rebounded. Those who were stopped out, however, reaped only huge losses with no chance to get back in before the rebound.

Similarly, the speed and power of Enterprise’s fall and rise suggests misuse of leverage on the part of many investors, either via margin or options. Use of either can boost returns under the best of circumstances. But on days like Mar. 15, investors are just as likely to get washed out, and at horrific prices.

Our strong advice remains not to use leverage on positions like Enterprise Products Partners. There is, however, a way to magnify your returns in solid companies without taking on these risks, by utilizing buy limit orders, set at “dream” prices.

One investor I know well was executed at $33.25 per unit on Enterprise on Mar. 15. He’s currently up 26.8 percent on that position. Anyone who got in at the day’s posted low is up more than 50 percent, for doing nothing more than entering an order to buy only when a specific price level is reached.

If you truly set a buy limit order at a real bargain or dream level, odds are they’ll sit unexecuted for long periods of time. But as we saw once again with Enterprise on Mar. 15, even the most dubious catalyst can set off a selling wave. And, ironically, conservative companies heavily held by fearful investors are most vulnerable to these one-day volatility events.

During Enterprise’s Mar. 7 presentation to analysts Chief Financial Officer W. Randall Fowler stated his view that investors should “never want to sell” his company. As long as this owner of energy infrastructure continues to perform–dividends have been raised 33 consecutive quarters–we have no argument with that. In fact, failing to make the numbers should be the only reason any yield-focused wealth-builder sells Enterprise.

And as long as the numbers are solid, any dramatic price dip–such as occurred Mar. 15 for Enterprise–is a massive buying opportunity. It may be a long time before these units again hit $35 per unit. But there’s no harm putting in a buy limit order there, either.