Two-thirds of baby boomers will inherit family money — a collective total of $7.6 trillion, according to the Boston College Center for Retirement Research. But much of that money won't last long. Nine of 10 family fortunes will disappear within three generations.

"The first generation makes it, the second spends it and the third starts over," says Gregory Dubnansky, a vice president with Beacon Trust in Morristown, N.J.

So how can family money survive the Three Generations Rule?

Have a tax strategy: Say dad has a $15-million portfolio of commercial properties. If he dies without proper tax planning, the tax liabilities could be huge, warns Dubnansky.

Rein in spending: Because the second and third generation didn't "earn" the money, "they tend to live extravagantly and make foolish investments," says Jerome Reisman, partner in the Garden City law firm Reisman Peirez Reisman & Capobianco.

Make them earn a living, says Andrew Smith, co-host of the radio program "The Mutual Fund Show."

Communicate: "Have multigenerational meetings with a financial adviser and estate attorney," says Cary Carbonaro, managing director of United Capital in New York City.

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At the meetings, family leaders should communicate their values and "wealth vision," says Haitham Ashoo, chief executive of Pillar Wealth Management in Walnut Creek, Calif.

Protect wealth: Says Dubnansky, the use of trusts, such as irrevocable life insurance trusts, can help control the access to and depletion of family funds.