“Sinatra Jr. could have avoided this mess in large part by having been more careful with his decisions and actions, chiefly by consulting with and listening to his attorney,” says Sleeth. “People need to be extremely careful that their actions don’t give their lover a basis to claim that the parties had a common law marriage.”

Rule number three is make sure to make provisions for those you want to take care of. In September, Florida Marlins pitching ace Jose Fernandez passed away at the age of 24 in a boating accident off the coast of Miami Beach. He was unmarried but his girlfriend, Maria Arias, was pregnant at the time of his death.

In order for the estate, worth millions, to take care of Arias, or at least the child, the couple would have needed to be married or Fernandez would have had to put money in a trust for the child. Or he would have at least had to agree in writing to give them a certain amount.

This case has not been challenged, but Sleeth says, “The scenario has all of the classic signs of what could make for a dispute.”

The fourth rule is exemplified by the case of author Tom Clancy, who was worth $80 million dollars when he died in 2013. The case was still prominent in the courts in 2016. Clancy had an estate plan for dividing the money among his second wife and his two sets of children. He also stipulated who should pay the taxes on the inheritance.

Shortly before he died, he signed an ambiguous codicil to the will, which led the courts to redistribute the multimillion-dollar tax bill among the children.

“The moral of the story is that estate planners need to be very careful about language that could arguably be construed as ambiguous,” Sleeth warns. “With an estate in the tens of millions, it was almost certain that all of the parties involved in Clancy’s estate would retain legal counsel who would pore over each word in his estate plan to seize on any ambiguity that could benefit their clients.”

Robin Williams’ estate ended up with a similar problem when the heirs argued over some of his clothing.

Sleeth says he has handled a lot of not-so-famous cases, including one involving a widower in Virginia who wanted to disinherit his children, who were spread all over the country. But he waited until shortly before he died to change his will. The children challenged the change, saying he no longer had the mental capacity to make those decisions.

“That case took years to litigate,” says Sleeth. “He should have made the change as soon as he decided to disinherit them, and not waited.”