If you provide estate-planning services to wealthy aging clients, there’s one detail you might not want to overlook—because many of your clients probably have. Although most wealthy Americans plan to leave their money to their children, and believe it’s important that the next generation manage wealth responsibly, few of them have written any incentives into an existing will or trust.

Those are the findings of a recent study by PNC Wealth Management, which surveyed over 1,000 adults with annual incomes of $150,000 or above and at least $500,000 of investable assets if employed, or with $1 million of investable assets if retired. According to the survey, 74 percent of respondents plan to leave money to their children, while 62 percent believe it’s important that each generation take responsibility for creating its own wealth; but, only 30 percent of wealthy individuals with estate planning documents have instructions that heirs must meet specific requirements in order to receive their inheritances.

“When it comes to leaving a legacy, too few individuals are taking the steps to ensure their heirs do not have unfettered access to their money,” says Martyn Babitz, senior vice president of PNC Wealth Management and a senior trust advisor. “With incentive trusts you can promote beneficial work and a valuable contribution to society as opposed to treating family assets as an entitlement.”

Nonetheless, the fatter the individual’s piggy bank, the more likely he or she is to take care that the inheritance left to a child will not go to waste. More than half (57 percent) of those with $10 million in assets and about 42 percent of those with between $5 million and $10 million in assets require heirs to meet certain requirements before that inheritance money falls into kids’ laps.

It’s also a practice that is more popular with the younger wealthy set. Over half (56 percent) of those aged between 18 and 44 have attached stipulations to their estates, compared with just 27 percent of those in the 45 to 64 age range and 19 percent of those over 65. “Younger people have younger children,” says Alan Aldinger, a spokesman for PNC. “Older people—their children are well into adulthood and may already have established more responsibility.”

Typically, the kind of stipulations attached to wills and trusts include reaching a certain age, attaining a certain level of education or holding a “productive” job, says Babitz. Some stipulate that the heir start a business or do work that is beneficial to society, like working for a charity. Others create disincentives aimed at motivating the heir to discontinue or avoid potentially destructive behaviors, such as abuse of drugs or alcohol.

Of those who had written incentives or disincentives into their wills, the survey found that 77 percent directed that the inheritance money be used for education. Another 46 percent required that the inheritance go towards basic needs, like housing. Some 29 percent set aside the funds for their grandchildren, 28 percent required that the inheritance be used for business or career-related expenses only, and just 16 percent stipulated that the inherited funds must be used for specific charitable donations.

Financial advisors who want to help clients write such stipulations in estate planning documents should be sure to consult good legal counsel. There are few restrictions a person can’t attach to an inheritance, says Phyllis Silverman, a senior trust officer for PNC. "So long as the restrictions aren’t illegal. For example, you can’t stipulate that the heir marry someone of the same race, or divorce their current spouse. But you can stipulate that the heir marry someone of the same faith." Still, trusts and wills are legal documents, so drafting them correctly is obviously important. "Errors in language can cause problems in interpretation, execution and taxation," she says.