My mum has a slightly unusual breed of dog. Her first was bought through the paper as an older puppy. The owners had originally wanted her as a show dog but one of their other dogs developed an illness and the puppy was too much for the older dog to cope with. One had to go, so the owners sold the puppy.
One day while out walking her dog, a passerby stopped my mum to admire the breed, comment on its unusualness, and happened to say 'mind you I saw another one at the local dog rescue.' Well my mum had to go and investigate, dog in tow, and sure enough there was an almost unrecognisable specimen, sad, skinny, matted fur, and scared of his own shadow. Except he made a beeline for mum's existing dog and then refused to leave her side. The workers at the rescue let mum take him then and there (usually they want to perform checks but they said that mum's dog was a testament to how well she could look after a new one, and it would be unfair to split the dogs even temporarily when the rescue dog had found a friend!)
They got him home, and he did nothing but cower in the corner. Out on walks he would cling so closely that the two dogs looked like one. And he barked at anything that moved, just in case it decided to attack him. He could only have been a few months old when he was adopted (still had puppy teeth) but we're pretty sure he was beaten by a man, possibly with a stick or other object, as he was particularly frightened of men and walking sticks.
Years later, he is a changed dog. He is still very nervous and prone to barking, but he can be walked (on a lead) in public and he knows some basic commands.
I'd like to take this opportunity though to remind people of the yellow dog scheme. The rescue dog wears a yellow ribbon to alert people to the fact that he is still nervous. He shows his nervousness by barking at people who talk to him or attempt to stroke him. My mum does her best to warn people not to do either of the above. But some people do ignore the warnings and attempt to stroke him and then are surprised when he barks (and a few have said they'll report him for being aggressive, which he isn't at all, he barks to defend himself from a perceived attack).
Please, if you see a dog with a yellow ribbon (or any dog for that matter) don't approach without the owner's permission, and of course teach your children not to either.