More than 1,000 dogs declared "dangerous" or "menacing" are living in Victorian properties, while a further 133 restricted-breed dogs are considered so high-risk they need to be kept behind 2-metre-high fencing.

Two days on from the mauling death of Mill Park man Leo Biancofiore, figures obtained by the ABC show 305 dogs listed as dangerous have committed previous attacks.

Animal Welfare Victoria figures show a further 179 guard dogs are declared as dangerous, while 689 are listed as menacing because of non-serious attacks or aggressive behaviour.

Restricted breeds include American pit bull terriers, along with the lesser-known perro de presa canario, dogo Argentino, Japanese tosa and fila Brasileiro.

American Staffordshire terriers, often confused for pit bulls, are also considered restricted if their owners do not have a pedigree certificate or a certificate from a vet.

The dog that attacked Mr Biancofiore and his wife, believed to be their son's American Staffordshire terrier, was not registered and the Whittlesea Council said it had received no previous reports about the animal.

Police and the RSPCA are continuing to investigate.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 16 seconds 16 s Man dies in Melbourne dog attack thought to involve American Staffordshire terrier

'It's very hard to define a pit bull'

Under Victorian law, it is illegal to breed or sell restricted dogs, and an owner can be jailed for up to 10 years if the animal kills someone.

These dogs must be desexed, microchipped, wear a special collar and must wear a muzzle if let off in public.

Warning signs must be placed at the property they stay in, which must have a perimeter fence at least 1.8 metres high.

Victorian laws were updated in 2017, following a four-year period during which pit bulls were not allowed to be registered and were destroyed purely because of their breed.

While the dogs were allowed to be registered again, the RSPCA and some lawyers remained critical because the laws continued to target specific breeds.

Leo and Donna Biancofiore were both attacked by the dog, Junior. ( Facebook )

Melbourne lawyer Brett Melke, who says he has represented clients and their pets in more than 500 cases, said focusing on individual breeds was "misguided".

"It's very hard to define a pit bull. There isn't a specific genetic test," Mr Melke said.

Other breeds must abide by similar conditions to restricted breeds if they are declared dangerous.

Dangerous dog declarations are usually made because the animal has committed a serious attack, or is a menacing dog that repeatedly escapes.

"In terms of dangerous dogs, I've had cocker spaniels, I've had golden retrievers, I've had jack russells and border collies," Mr Melke said.

Genetics and environment behind attacks, RSPCA says

American pit bulls owners face potential jail terms if their dogs commit attacks. ( Flickr: DeeMo )

The RSPCA's head of operations, Tegan McPherson, said her organisation backed a "deed-not-breed" approach to judging animals.

"Breed alone isn't a reliable predictor of aggressive behaviour," she said.

"It can be influenced by genetics, learning experiences and training and its environment.

"You've got American Staffies that are wonderful family pets, but you also have ones hitting the news for the wrong reasons."

Mr Melke and Ms McPherson said it was vital owners registered their dogs.

"There should be some kind of incentive system for people to register dogs," Mr Melke said.

"When dogs are unregistered there's no way to track what they're doing, there's no way to track where they are. It's a dangerous scenario."

Staffies struggling to find homes

American Staffordshire terriers are wonderful family pets, according to the RSPCA. ( Flickr: Corinne Benavides )

Staffordshire bull terriers and American Staffordshire terriers regularly fill spots in council pounds and adoption centres around the country.

When the ABC attended an RSPCA pop-up adoption event in Brisbane last year, about three quarters of the dogs looking for a home were so-called "bully breeds".

Ms McPherson said it was unclear why higher rates of the breeds were being discarded.

"We've been wanting to look at why these animals are coming to us and what we can do in the community around education and support," Ms McPherson said.

"They are a breed that tends to need a lot of engagement and enrichment and exercise."

"There may be a misunderstanding of what that breed requires."

Professor Paul McGreevy, an expert in animal behaviour and welfare, was more blunt with his assessment of some owners.

"Unfortunately for Staffordshire (bull) terriers, many muscular breeds have attracted an unhelpful fan-base among people who feel their dog should reflect their personal machismo," he said.