If you want to make good in the bear-canister business, you go up to Folsom with hat in hand and pay your respects to Fisher — a larcenous, no-neck, knuckle-dragger who could take your face off with a lazy flick of his wrist.

Fisher is a 580-pound black bear. He used to be what wildlife types call a "problem bear," snatching fish guts and scaring anglers at a fish-cleaning station near Bridgeport in the eastern Sierra Nevada. Now he is a quality-control expert at the Folsom City Zoo Sanctuary — stomping, whacking and ripping with his massive jaws the cans, bags and boxes designed to keep backpackers' food away from hungry bears in the wild.

One of the big tests for a new product is an hour with Fisher. If he manages to smack open a supposedly bear-proof receptacle loaded with goodies, it will be rejected by a committee of park officials called the Sierra Interagency Black Bear Group. But if Fisher can't crack it, officials will endorse it for use by the tens of thousands of hikers who trek to Yosemite, Sequoia and Kings Canyon national parks and the Inyo National Forest each year.

"He's sent many an inventor back to the drawing board," said Roberta Ratcliff, a zoo spokeswoman. "He's a pro."

Fisher is a key player in the small but growing industry devoted to thwarting hungry bears. In areas of the Sierra that draw a lot of backpackers, bears have gotten wise to the old camping precaution of dangling a sack of food from a rope or tree limb. Now they make quick work of nylon bags filled with candy bars and freeze-dried beef stroganoff, crawling out on flimsy branches and swiping at ropes with the skill of pirates scooting up to a crow's-nest.

As a result, campers in some bear-rich national parks and forests in California, Washington and Alaska must tote food canisters that bears can't open or risk a $150 fine.

The market is dominated by bulky, drum-like cans that cost $60 to $200. Many hikers find them to be a pain in the backpack, but their discomfort has put entrepreneurs on the scent of opportunity. In Santa Barbara, retired aerospace engineer Allen DeForrest and two longtime colleagues mortgaged their homes to develop a lightweight canister called the Bearikade.

In three tests, Fisher punctured the space-age composites used to make the prototype Bearikades, succeeding where two grizzly bears at the Fresno Zoo had failed. The Fresno bears, Betsy and Ross, had scrutinized a Bearikade smeared with blood and filled with rotting meat, carefully inspecting it for seams and even tipping it on its side to expose its weakest point.

"They went at it kind of like engineers," DeForrest said. "Fisher used brute force. He had no regard at all for his teeth or his gums or his lips."

DeForrest eventually thwarted Fisher with an improved design, but San Francisco attorney Tom Cohen hasn't been as fortunate.

Bulletproof Kevlar

A few years ago, Cohen, who once hauled a heavy canister over the 211-mile John Muir Trail, invented the Ursack, a lightweight, scrunchable bag initially made of bulletproof Kevlar. A bear in the Adirondacks shredded an early Ursack, so Cohen found a stronger fabric and had it sewn with even tighter seams.

Then came Fisher.

Cohen poured a quart of honey into his new, improved Ursack, added some bagels for heft and looped the bag's Kevlar cords around a concrete post in Fisher's den. When Fisher lost interest after grappling with it for just 3 1/2 minutes, Cohen jubilantly declared a technical knockout.

But officials with the interagency group turned down Cohen's bid for approval, citing five punctures from Fisher's teeth. Cohen pointed out that Fisher, who goes unfed before his testing sessions, didn't bother to suck the honey through the holes.

"If we can ever get them to change their minds, we'll have a real business," said Cohen, who has hired an attorney and is considering a lawsuit.

Texas engineer Bruce Warren, the inventor of a canister he calls the Stealth Can, is also frustrated, contending he could sell "jillions" of units if the interagency group were more open to innovation.

Warren readily admits that any bear could slice the Stealth Can like a tomato. But, he says, bears won't even approach the can, which ordinarily is used for hazardous waste, because its vacuum-sealing lid traps all food aromas inside. The cans, loaded with Oreo cookies and other delicacies, sat on a New Mexico trail untouched for two weeks as bears padded by, Warren said.

But Harold Werner, an ecologist at Sequoia and Kings Canyon national parks, as well as a founder of the interagency group, was skeptical.

"No matter how good the seal is, you'll still have food odors associated with it," he said. A greasy fingerprint on the outside of the can would be enough to draw a hungry bear, he added.

Bears have an extraordinary sense of smell — more than seven times sharper than a bloodhound's, by some estimates.

That makes wildlife biologists like Tom Smith all the more astonished by the chutzpah of some outdoorsmen when it comes to storing food.

"Some of these people!" said Smith, a bear expert with the United States Geological Survey in Anchorage. "One guy in a field camp tied some bacon to the center pole of his tent so he and his buddy could defend it if they had to. He woke up one night with a bear standing on his back, and his friend shot it."

Tug-of-War

Last year, a bear in Yosemite snagged Michael Stanfield's food bag and the long rope it was hanging from. Grabbing the rope's other end, the 55-year-old Jamestown carpenter engaged in a futile tug-of-war with the beast.

"I was being a bit of an idiot," admitted Stanfield.

That night, he hung his backpack with his few remaining provisions, including a grapefruit, from a higher limb and slept at the base of the tree. In the morning, he realized that tactic had also been a mistake when he discovered a cleaned-out peel only inches from his head.

In Yosemite, Sequoia and Kings Canyon, bears jump on car roofs, pry off doors, shatter windshields and rip up back seats to get at food stored in trunks. In Yosemite five years ago, hungry bears staged a months-long demolition derby in parking areas, smashing open more than 1,300 vehicles. The number dropped to 306 in 2000 after rangers started requiring the use of bear-proof food lockers at campsites.

Rick Agnelli, a camping-goods salesman at Recreational Equipment Inc. in Northridge, saw the flattened wreckage after a notorious bear at Yosemite flung himself on a tent "to see what would come out." Fortunately, the tent was unoccupied.

A few years ago, a bear rifled Agnelli's backpack as he slept. Although Agnelli had stored his food in a bear-proof locker, the bear nonetheless ripped through every plastic bag it found in the pack.

"They were just extra bags, but the bear associated them with food," Agnelli said.

Because bears associate food with people, "they simply pursue people with a ready source of food," said Werner, a 23-year park veteran who one year early in his career was forced to shoot seven bears that were deemed incorrigible.

With hundreds of encounters between humans and bears occurring in the Sierra each year, wildlife officials over two decades have tried to increase safety for both.

Engineering Challenge

In the early 1980s, they turned to Richard Garcia, owner of a machine shop in nearby Visalia. His assignment: Come up with a way to keep human food out of ursine paws.

Today, Garcia's company is the oldest and biggest maker of bear canisters.

"It was a real engineering challenge," he said. "You had to make them light, but also big enough to keep a bear from getting his jaws around them."

Garcia's first models were 5 pounds — a millstone to backpackers, who aim to shed every needless ounce. Today, Garcia's canisters are made from highly durable plastic and weigh 2.7 pounds. Campers usually unlatch them with a coin — a technique well beyond the average bear. "You have to outsmart them," Garcia said.

At the Folsom zoo, Fisher has more than once used his mighty legs for leverage after tossing a canister into his pool, jamming it into an underwater crack and bending down to grab it between his jaws.

Although he has a couple of understudies who also test canisters a couple of times a year, Fisher is still the king.

Stories about him abound. There was the time five grunting men carried a jam-packed, bear-proof food locker into his den. With one colossal paw, Fisher sent it sailing. The zoo's Roberta Ratcliff said she has seen him extend his arm through hard plastic into a picnic cooler.

"He didn't pop off the lid," she said. "He just reached in."

At Sequoia and Kings Canyon, Werner has seen bears like Fisher in the wild more times than he can count. Little wonder that he vacations in the desert or at the beach — anywhere but bear country.

"My car must reek of food," he said. "Why take the risk?"