Dog Park Etiquette

I have been meaning to write this post for a while. Tonight pushed me over the edge. I have a 13+ year old dog who is literally on her last legs. Luckily I live across from Highland Park in the Fort Hill neighborhood of Roxbury. Since I moved in over 2 years ago I have been walking Ramona at Fort Hill everyday. There is a small dog community who let their dogs off leash up there. A majority of them are very nice. I keep Ramona on a leash most of the time because she cannot really run anymore, but in her prime I used to run her at dog parks all over the city: Franklin Park, Peter's Hill, Fresh Pond, S. End etc.. When a dog owner takes their dog to these parks there are certain behaviors or etiquette that most people follow: picking up after their dog, controlling barking etc.. One of the most important ones is that if your dog is running towards another dog or person please let me know if they are friendly. It is really a safety issue. This seems to have been lost some of the nice people of Fort Hill. There have been numerous occasions when a dog has rushed Ramona and the dog owner says nothing. Twice I have actually asked if a dog was friendly and got nothing as the dog proceeded to be aggressive towards Ramona. It is kind of scary when a dog you do not know runs towards you.
There is also a set of dog owners in the park who own a dog named Jazzy. This dog is never on a leash. She is walked by two different men. They seem to know a lot of people in the park and Jazzy is a very exuberant dog. I also think they breed her and other people in the park have adopted the puppies. She is a large boxer. This dog has attacked Ramona at least 6 times, pinning her down on two occasions. This dog has also attacked other dogs I know and drew blood. When ever I see the owner in the park I tell him Jazzy is aggressive to my dog and he does not seem to care. He never puts her on a leash. When I yelled to him across the park tonight as I try to avoid him and he yelled at me and told me not to threaten him. All I said was, "Your dog is aggressive to my dog and has attacked her numerous times, my dog is on a leash." He also went into how he has been living the neighborhood longer then I have been alive and just keep walking my dog and mind my own business. Another dog owner he was with slunk away as he continued to argue with me and basically call me a liar. Jazzy does play with other dogs in the park and is fine, but she does not seem to like Ramona very much. There is another dog in the park who also has problem with female dogs and that owner immediately takes control of her dog when she sees us and we have a great relationship. In all my dog owning years I have never met a dog owner who does not seem to care that their dog does harm to other dogs and a dog community to supports that behavior. Every other dog park I have ever been to would never put up with such bad dog park etiquette. It is unfortunate because the park is really a hidden gem.