A pervert who made an obscene suggestion to a woman walking in a park was savaged by her Alsatian.
The dog sunk its teeth into his forearm after he lunged towards the woman.
The animal let go of the man only when the woman - who by this point had run off - called the dog.
The attack happened on Sunday night in a park in the Harrowgate Hill area of Darlington, County Durham. The woman is in her forties.
Pc Astrid Chapman said: "The lady let the dog off its lead and was watching him as closely as she could in the dark when she became aware there was someone behind her.
"She turned around and saw a man directly in front of her. He moved his arms suddenly, but she can't say if it was an attempt to grab her.
"He then made an obscene suggestion. He made it with such aggression that the victim was rooted to the spot with fear.
"At that point the dog, which is extremely protective of its owner, started barking and growling and baring its teeth.
"The dog then lunged at the man and clamped his jaw around his right forearm. He held him despite the man's violent attempts to shake it free."
The woman ran away as the man was struggling with the dog. She then shouted for the animal once she was at a safe distance and it released the man.
He ran off in the opposite direction.
Police have been monitoring hospitals and health centres to see if anyone comes forward seeking treatment for animal bites.
The man is described as white, in his thirties, between 5ft 8in and 5ft 10in, and of stocky build. He was wearing a dark woollen hat and a dark padded jacket.
Pc Chapman said: "The woman was unhurt but extremely shocked and upset by this.
"At the point of confrontation the man's eyes were described as being extremely wide and bulging.
"We have been making inquiries at local doctor's surgeries to see if anyone has sought treatment for injuries like the ones this man would have sustained.
"We would like to hear from anyone who would be able to identify this man, or who might have seen him in the area immediately before or after the incident."