The most recent law, signed in April by Florida's governor, takes effect in January.

The average amount left to pets is about $25,000, says Lawyers Weekly USA, a trade journal that has surveyed pet lawyers.

The pet trust laws buck centuries of legal precedent frowning on the practice, in part because the trusts have no human beneficiary. But unlike other recent attempts to expand the legal standing of pets and other animals, the pet trust movement largely has been without controversy.

"This is clearly an idea whose time has come," says Gerry Beyer, an estate law professor at St. Mary's University in San Antonio who has written about pet trusts.

"The idea (of a trust fund for a pet) has gone from something that seems laughable to something that's very mainstream, almost overnight," Beyer says.

Americans own a huge number of pets, including about 68 million dogs and 73 million cats, according to a 2000 estimate by the American Pet Products Manufacturers Association. The impulse to protect them after one's demise has always been strong and, for some, overwhelming.

In 1993, tobacco heiress Doris Duke left $100,000 to her dog Rodeo, a Shar-Pei. A will written by actress Betty White is reported to leave all of her $5 million estate to her pets. And British singer Dusty Springfield's 1999 will specifies that a bequest for her cat Nicholas be spent on a lifetime supply of his favorite meal, imported baby food.

Courts have often invalidated such trusts because they were considered excessive or because their duration was not based on a human life, a traditional measure for a trust.

But a 1993 change in the Uniform Probate Code, a legal model used by many state systems, allows trusts for pets that continue for the pet's lifetime. The states quickly followed with laws of their own.

Now, by adding only a sentence or two to an ordinary will, pet owners can designate an amount to be spent on the pet and a trustee to carry that out under court supervision.

In three of the 16 states with pet laws — California, Missouri and Tennessee — trusts can be set up, but the trustee is not legally required to carry out the terms.

Lawyers Weekly editor Paul Martinek estimates that "dozens if not hundreds" of pet trusts have been set up under the new laws.

Pet trusts are not without drawbacks. Animals can't complain to a probate judge if their trustee is shortchanging them on food or accommodations. And a dishonest trustee could fraudulently extend the life of the trust to continue receiving a trustee stipend.

Beyer has written of a San Francisco maid who was appointed trustee for an ordinary looking black cat. When the cat died, the woman adopted a look-alike to keep the trust fees flowing. She was on her second replacement cat before she was detected.

But pet laws do take into account one key fact of modern life: Surviving adult children may be reluctant to carry out a parent's final wishes.

"If it was just you and your pet, and you weren't so sure that your kids halfway across the country would take them, the only way you might get peace of mind is by (setting up a pet trust)," Martinek says.