NEW YORK (TheStreet) -- In a quest to achieve a life-long retirement income, investors worry about how much to spend, as well as how to protect their precious portfolio. Typical investment mixes can include a “balanced” portfolio -- evenly split between stocks and bonds -- or an “income” portfolio of all, or nearly all, bonds. There are countless other allocations to consider, as well.

Once properly invested, retirees are frequently reminded of the “4% rule”: Withdraw up to 4% of the portfolio’s value annually, no more. But with low-interest rates impacting portfolios, the 4% rule has become a sometimes broken rule of thumb.

A couple of years ago, Jason Scott and John G. Watson, researchers at Financial Engines in Sunnyvale, Calif., developed an alternative investment mix: the floor-leverage strategy, saying the portfolio “strikes a balance between precision and simplicity.”

“The floor-leverage rule is a spending and investment strategy designed for retirees who can tolerate investment risk but insist on sustainable spending,” the researchers wrote in September of 2013. “The rule calls for purchasing a spending guarantee with 85% of wealth and investing the remaining 15% in equities with 3× leverage. Surprisingly, this leverage is a tool for managing risk.”

Leverage is, in effect, borrowing money to multiply an investment. Three times leverage triples the result: positive or negative. It’s not for the faint-hearted. But, in this case, 85% of the portfolio is in “safe money” – Treasuries, government bonds, a “late-life” annuity – or perhaps even cash considering today’s shaky bond market. The remaining 15% is supercharged by using leveraged ETFs or mutual funds.

Georg Vrba, a consulting civil engineer living outside of New Haven, Conn., believes the floor-leverage strategy was a seed of an idea that needed improvement. He contends mathematical models can predict the stock market better than financial "experts.” Vrba calls his modification of the strategy the floor-surplus portfolio. It still utilizes leverage, but tactically – moving in and out of the oversized stock market bet as market signals indicate.

The floor-surplus portfolio uses the UltraPro S&P 500 ETF (UPRO) - Get Report for the 15% allocation to a 3x-leveraged investment – but only for those periods when technical indicators favor exposure to stocks. When the stock market looks to be turning against the tide, it is replaced with (IEF) - Get Report, the iShares 7-10 Year Treasury Bond ETF.

This is where things may get just a bit sticky for the average investor. Vrba is timing his stock market exposure on “buy” and “sell” signals. He believes a sell signal occurs when the 40-day simple moving average (MA) of the S&P 500 crosses below the 200-day MA.

Don’t know what all that means? His website,, shows you the chart once you register for free. Of course, premium services are also available, but he says the S&P 500 moving average crossover model (MAC-US) will always remain free to registered users, with data delayed by three days.

It’s not an indicator that changes very often. Since January of 2010, there has been a grand total of two sell signals and two buy signals. The last “buy” signal was issued three and a half years ago, and Vrba says we’re still in a “buy” mode – and nowhere close to a “sell” sign. Of course, he quickly admits that no technical indicator can predict “Black Swan” events like the ’87 stock market crash.

But aren’t investors constantly told, “Don’t time the market”?

“I don’t believe in that,” Vrba said. “The moving average crossover system is a very slow (indicator). People have back-tested this to the 1880s. It definitely works. It's not going to take you out at the top. It's not going to bring you back into [the market] at the bottom. But for the investor that wants to move their money slowly, in my opinion, it works well.”

In a back-test analysis Vrba completed in July of last year, the Floor-Surplus portfolio allowed an annual withdrawal rate of 6.5% from January 1999 to June of 2014, while preserving principal. The original Floor-Leverage portfolio allowed a 3.25% annual withdrawal rate. Even though it is an attempt to “time the market,” considering the typical 4% withdrawal rule of thumb, perhaps Vrba’s time has come.