Even if two funds have a similar equity allocation, there may be big sector differences underneath.

"We knew that at some point in the cycle there would be an equity correction and people would address their equity allocation," Mr. Kirsch said.

Accordingly, we are dropping our equity allocation to 55 percent from 60 percent and raising the cash position to 20 percent from 15 percent.

Last week, the firm increased its equity allocation to 91 percent, reducing cash to 9 percent from 15 percent, Mr. Sichel said.

If those things were to substantially erode from where they are right now, we would probably lower the equity allocations more.

But if they were to improve, we would raise the equity allocation.

We recently lowered our equity allocation.

And if they can do that, when they are older, they can cut back on their equity allocation.

To ensure some discipline, Mr. Evensky suggests investors put the bulk of their equity allocations, the core, in a low-cost, broad-based index fund.

This satellite allocation may be implemented into 100% equity allocations and/or allocations that blend with fixed-income or non-equity positions.