A Vietnam veteran has been left in agony after a frightening dog mauling.

The great-grandfather from Mandurah fell during the attack, breaking a bone, but the 75-year-old says he doesn't want the dog destroyed.

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Brian Dillon has had four knee replacements but he says nothing compares to the pain of his mauling injury.

"That would be the worst injury I've ever had in my life," he told 7NEWS.

He was attacked by the dog at a Dawesville boat ramp last Wednesday night and says the pain just won't go away.

Chevron Right Icon 'That would be the worst injury I've ever had in my life.'

Mr Dillon estimates the dog weighed around 50 kilograms and the force of it latching onto his arms made him fall off the side of the jetty.

Nightmares

He is struggling with the emotional as well as physical ramifications of the attack, waking up in the middle of the night screaming after having nightmares.

While the dog's owner came over to see if he was alright, he didn't give his details.

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The City of Mandurah told 7NEWS it was investigating the incident.

Mr Dillon believes if the dog had attacked a child, the outcome could have been much worse, but the animal lover doesn't want the dog put down.

Spike in attacks

Since July, there have been 143 dog attacks reported to Mandurah rangers - 23 more than at the same time last year.

Animal behaviour experts say the worst thing you can do if you're about to be attacked is to turn your back on the animal.

"Keep them in sight and move slowly backwards," Dr kate Lindsay from Kalmpets Animal Behaviour Centre says.

"Avoid shouting, hitting, or kicking.

Chevron Right Icon 'Avoid shouting, hitting, or kicking.'

"There's no such thing as an aggressive dog, there's just frightened ones.

"So the dog is just as frightened as you."

Mr Dillon's message to dog owners is simple: keep them properly restrained when out in public.