"Fulfillment" is the newest buzzword among dog lovers, who increasingly seem inclined to figure out what their dogs were born to do--and then attempt to let them do it.

Herding breeds must herd; hunting breeds must hunt, and so on. The idea is that when dogs satisfy their biological imperatives, they will feel Fulfilled and therefore be more even tempered, obedient, have a more positive attitude.

Now we hear the F-word from Cesar Millan, who runs a rehabilitation center for delinquent dogs--a kind of last-chance boot camp for three-strikes canines who fight, bite, run away and disobey.

Millan, 27, owns the Dog Psychology Center of Los Angeles--a 2-acre clinic in a downtown warehouse, where he guides unbalanced dogs back to happy, productive lives. He talks like Freud, looks like Rudolph Valentino and acts like Merlin the wizard when his deep, silent stare causes peace to descend upon even the most unhinged of his quadruped clients.

He spends at least four hours a day hiking the nearby hills with a pack of 30 unleashed, highly aggressive dogs trailing behind him. They are his patients. And they are plagued with problems that range from moderate antisocial behavior to belligerence that puts them in what Millan calls "the red zone." That is: They plunder, pillage, maim and maul.

But they can all be healed, he says, if only we start Fulfilling their needs. "If a high-energy dog is not fulfilled," he becomes aggressive and will not obey. "It is like with people. When a man wants his woman to cook for him, he has to learn to fulfill her needs before he can ask for such a thing, no?"

No comment. Millan is married to the lovely Illusion, also 27, who works with him. He says he has had to learn more about humans than about dogs, who were his closest companions from the day he was born in Mazatlan, Mexico, and all the while he was growing up. "I literally lived, slept, ate and played with dogs all my life. My grandfather and father knew all about dogs and gave their knowledge to me."

Treatment starts daily at 6 a.m. That's when he loads the van with the pack and drives to one of many nearby sylvan spots where he does therapy. A hillside road near Avenue 52 in Highland Park is one of his favorites. There, he power-walks uphill, nonstop, at precisely 3.5 miles per hour--the perfect pace to keep the dogs focused on him as they expend their abundant energy, he says.

"On this typical route, we walk to the top, which takes an hour. We stop at a lake, where the dogs cool down. They swim. They relax. After 30 minutes, we walk for another hour. We enter a wooded area, where I allow them to relieve themselves in the trees. They have exactly five minutes to come back for formation. I walk again for an hour, and they follow. A pack leader doesn't have to talk. When he moves, so does his pack."

They stop to play ball for 30 minutes--there's one ball in his backpack for each dog. Then Millan follows the same routine going downhill and piles the 30 animals into his 15-person van.

Back at the center, he inspects for cuts and ticks, massages their muscles, gives them a three-hour nap before they are fed.

"This is not training. That's not what we offer. This is rehab," he says.

"People send dogs to me as a last resort. They cannot live with them anymore." Most of his patients come from very good homes, Millan says. They have had the best of everything: food, toys, trainers, indoor and outdoor space. But they are still so dangerous and ill-behaved that they are on the brink of being considered unfit to live. And that is because their needs have not been met. They are not Fulfilled.

The dogs of homeless people are much more fulfilled than the pampered dogs of Palos Verdes and Beverly Hills, Millan says.

"You never hear on the news that a homeless person's dog has run wild or attacked. And most of those dogs aren't even on leashes," he says. "But they follow their leaders everywhere. That's because every day is a new challenge, an adventure. They walk to new places, see new things, their minds are focused, their bodies active. That's what they need. Exercise first, then discipline and then love."

And when they walk together, Millan adds, you almost always see the homeless person in front and the dog behind him or at his side.

But go to almost any upscale neighborhood, Millan says, and you'll see the dog on a leash, in front of the person who's walking him.

"Position means a lot. If the dog is in front, and you are in back, you are the follower. You have no power over him if he gets excited or anxious. Dogs don't listen to followers. They need to be led."

Millan says even a palace can be a prison for a pooch. A woodsy fenced acre can feel like county jail. "No matter how big the yard, it is like a penitentiary because it is already familiar, and it has walls the dog cannot get beyond." His frustration level builds up. He starts to have ... issues. And you do the dog no favor by taking him from the house to the doggy day-care place to play, Millan says.

"It's like taking a tiger from one zoo to another zoo."

Leslie Rankin, who is registrar at the Ronald Reagan Presidential Library in Simi Valley, is one of Millan's clients. Her 5-year-old coon hound, Elvis, is a 75-pound, powerful specimen of a hunting breed who became "the sticking point" in her divorce, she says.

"We both loved him and didn't want to give him up. We had different ideas of what was best for him." Both knew that Elvis needed an attitude change--or else.

"He was already on heavy tranquilizers, and even that did no good. He was so aggressive and mistrustful of strangers that we couldn't have guests at our house." He bit Rankin on the face and foot, she says, and bit her ex-husband too. After she got legal custody of the dog, she took him to Millan, who kept him for five weeks.

"Elvis comes home. He's totally changed. He's happy. He likes people. He knows how to play with other dogs. People are no longer afraid of him. He kisses them." Rankin says she considers Millan the dog world equivalent of the woman who taught Helen Keller. "Cesar was able to break through to the Elvis that I knew was inside."

Millan's clientele includes the dogs of many actors and directors (such as Ridley Scott, Rebecca Romijn-Stamos, Will Smith), as well as some low-income dogs who've landed in shelters where their bad behavior makes them impossible to place. The shelters send them to him for rehabilitation so they can find homes. He charges private clients $40 to $80 per day, depending on the dog's diagnosis.

Donna Koch, a lawyer for Los Angeles County, rescued Rusty, a starving mixed-breed mutt that her sister had found. He was aggressive, didn't like people he didn't know, couldn't get along with the other two dogs in her home.

"At the park, he would go nuts and try to attack strange dogs. We got trainers for him, but that didn't work. We were desperate for help."

A friend told them about Millan, who came to their house. He showed how to make Rusty more secure, through exercise and discipline. "Basically, we had to demote all three of our dogs to pack-member status, with my husband and I as their leaders. This worked."

They and their three dogs spent several sessions hiking with Millan and his pack. "We saw a different Rusty start to emerge. He began to relax, to walk with the other dogs. He wasn't fearful or angry anymore."

Millan, she says, "has a gift. I hate the word 'awesome,' but that's what he is. He communicates across species without saying a word. We wanted Rusty to live. He made that possible."