After several months of rising markets, it seems investors may finally be starting to get nervous about the future. Over the last several weeks, billions of dollars have flowed in money-market funds, with net inflows totaling $30.9 billion for the week ending Aug. 9, according to Lipper Fund Research. In the two weeks prior, net inflows totaled $18 billion and $10 billion, respectively.

The S&P 500 itself is only up 0.3 percent over the last month, while the market is down about 0.5 percent since Aug. 8, when Donald Trump promised to bring “fire and fury” to North Korea if it didn’t back down on its bombing threats. The CBOE Volatility Index (VIX), which measures market volatility, is also up, climbing 24 percent since Trump’s Korea comments.

Karen Schenone, U.S. iShares investment strategist, has seen investors move into safer investments as talk of nuclear war with North Korea has ratcheted up. North Korea leader Kim Jong Un’s threat to fire missiles at Guam has increased fears. “We do see markets react whenever there’s geopolitical concerns,” she says. “We have been seeing a small flight to quality occur where people go to the safest assets they can find.”

The S&P 500 has recaptured some of those losses — it rose 1 percent yesterday — but with North Korea still in the news, tensions among Americans rising, and growing uncertainty over whether Trump’s tax-reform agenda will pass, money could continue to flow into less risky assets.

For jittery ETF investors who want to move into more cashlike products but don’t want to sell their securities to buy low-yielding money market funds, there are ways to reduce risks.

The first step is rebalancing, says Yves Rebetez, managing director of ETF Insights, a Toronto-based ETF education company. Since January, the S&P 500 has climbed 10 percent, likely putting many people’s asset allocation out of whack. Simply selling some equity ETFs and reallocating that money into bonds will go a long way to safeguard a portfolio.

“With equities at pretty much all-time highs and valuations extended, the first step to becoming more cautious would be to rebalance,” he says.

After that, investors could consider money market–like ETF options — ETFs that invest in extremely short-term treasuries — but with most paying next to nothing, a shorter-term bond fund may make more sense, says Alex Bryan, director of passive strategies research at Morningstar.

He suggests looking at the PIMCO Enhanced Short-Term Maturity Active ETF (MINT), which acts almost like a money market fund but invests in slightly longer-dated treasuries and corporate bonds. Its average duration is 0.39 years, and it has 1.54 percent yield, while most money market funds have a 90-day duration and pay less than 1 percent.

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“It invests in securities that are just beyond the reach of most money market–fund managers,” says Bryan. “So it gets more yield by going a little longer on the curve.”

Another option is to allocate more money to a broad-based bond fund, like the Vanguard Total Bond Market ETF (BND), which holds 8,137 bonds, about 64 percent of them government issues. With an average duration of 6.1 years, it has a decent 3 percent yield, but it’s not too long dated to be impacted significantly by rising yields, which can cause bond prices to fall.

“It should be able to weather market volatility better than lot of active bond funds, which do take on a bit more credit risk,” says Bryan.

When it comes to your equity allocation, any significant market downturn will impact the stocks you hold. However, there are ways to protect yourself in more up-and-down markets.

Over the last few years, several companies have introduced low-volatility ETFs, which are actively managed smart-beta securities that typically hold more conservative companies, often large-cap defensive names. Studies have shown that they do fluctuate less than the overall market.

“It goes back to the idea that when times get trickier, you may want to focus on a basket of stocks that are shown to be more resilient and less volatile to the downside,” says ETF Insights’ Rebetez. “You want companies that have higher intrinsic qualities in terms of balance-sheet strength and stability of profits.”

While there are plenty of options to choose from, Bryan likes the iShares Edge MSCI Minimum Volatility USA ETF (USMV). It tries to create the least volatile portfolio possible from a broad set of companies, and it limits sector tilts and turnover, he says. That helps the fund hold up in down markets.

Those worried about how geopolitical issues might impact global sales could consider limiting exposure to international businesses, or American ones that derive most of their revenues from outside of the country.

Last week BlackRock launched the iShares Russell 1000 Pure U.S. Revenue ETF (AMCA), which invests in companies that derive at least 85 percent of its revenues from the United States. “That’s another way investors can insulate themselves from geopolitical events,” says U.S. iShares investment strategist Schenone. “Stick to more pure-play U.S. companies.”

Investors can also move some money into gold, which has traditionally acted as a hedge against falling markets, says Rebetez. Gold often climbs when stocks fall, and indeed, the yellow metal has risen by nearly 2 percent since Trump’s Aug. 8 comments. However, Bryan says to be careful with gold and gold ETFs, as they don’t provide a yield and prices can fall quickly if market sentiment changes.

While it’s reasonable to reduce risk in a portfolio based on geopolitical concerns, changes should be done mostly at margins, says Schenone. People tend to move too much of their money into cash when they get nervous, then end up not earning anything on their investments.

“If you’re sitting in cash, you’re not keeping up with short-term market yields, and that will reduce the purchasing power of your savings,” she says. “If you’re getting nervous about the markets, at least invest in something that can take advantage of the market instead of sitting on the sidelines.”

— By Bryan Borzykowski, special to CNBC.com