Off lead walks with scary dogs

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So this lady in my neighbourhood walks her massive untrained dog down the street. He barks the whole walk long and runs along a few metres ahead of her. He goes down into peoples yards, I have even seen him standing at a neighbours glass window looking in. One time I was sitting in my car waiting for someone and the dog walked by saw someone was in the car and body slammed it. It's against the law here to walk dogs off lead so I know it's not something you're supposed to do and it makes me wary taking my dog out for a walk when this one is around. Is this something that would concern you if you are a dog owner? Is it ok and I'm over-reacting or do you think the owner is irresponsible? Note I don't actually think this is a bad dog or scary as such, it's just untrained.