Dr. Marty Becker and Gina Spadafori have the week off. This article originally appeared in November 2004.

About once a month, I'll get a frantic e-mail from someone who's frustrated to the point of desperation.

"Help!" the e-mail will scream. "I have a Jack Russell, and he digs, barks and chews when we're gone. He's too hyper! We can't take it anymore!"

Sometimes, it's all I can do not to write in return: "High energy? Digging? Barking? Chewing? Congratulations! You have an authentic Jack Russell terrier! What did you expect?"

What they expected, of course, was an adorable, low-key and well-mannered small dog, like Eddie on the TV show "Frasier" or Wishbone on the PBS children's series of the same name.

What they don't know is that Moose, the dog who played Eddie, had a full-time trainer, or that the role of Wishbone was played by several well-trained dogs.

And what about their cute little hellion? Perfectly normal for any Jack Russell who isn't given the structure and the physical and mental exercise these hard-driving dogs need.

"I get those phone calls every day," says Margie Kauffman, past president of the Northern California breed club who has been active in finding new homes unwanted Jacks. "They're mostly from folks who haven't done their homework and don't know of the breed's natural tendencies. The Jack Russell is a working terrier, with lots of energy and tenacity.

"These dogs are loving, loyal and very smart. But when they're bored … they're destructive," she says. "In my own pack, they're not bored. They get lots of exercise, and they're engaged all the time."

Lyndy Pickens got her first Jack (which the American Kennel Club calls Parson Russells, by the way) at the age of 3 and vows to have one as long as she lives.

"They're thugs in clown's clothing," she says. "This is not a dog bred to ask permission."

Indeed, knowing what the Jack Russell was bred for is essential to understanding how to keep both a terrier and your sanity, says Kauffman, who has seen thousands of Jack Russells over the years. ("My daughter calls me the patron saint of Jack Russells," she says, laughing.) "If you look at any dog breed, they were bred for a specific purpose," she says.

"Jack Russells weren't bred to be pets. They were bred to work: 150 years ago, the dog would have been everyone's household vacuum. Bugs, mice, rats – people didn't want pests in the house, the barn or the chicken coop. The dogs had to work for their keep, killing the pests. They're not like a cat, who will eat and then not hunt again. The Jack Russell will keep killing.

"Jack Russells today are hardworking, tenacious little dogs as a result."

So why are these dogs so popular? When living with people who understand them, who keep their minds and bodies exercised, who train them and work them constantly, who set limits and gently but firmly enforce them, the Jack Russell is an outstanding companion.

"I love how joyous they are," says Pickens. "It's interesting to live with them," says Kaufman. "They're bright."

For people who understand the breed and are willing to work to keep a working terrier happy, there's no better dog in the world. But if you want a lazy dog or an easygoing dog for beginners, you're better off without this breed.

Pet Connection is produced by a team of pet-care experts headed by veterinarian Dr. Marty Becker and journalist Gina Spadafori. The two are also the authors of several best-selling pet-care books. E-mail them at petconnection@gmail.com or visit www.petconnection.com. Back columns: www.sacbee.com/spadafori.