I saw a horrible incident once. An aggressive dog, unsupervised picked up a little dog with its mouth and began to violently shake the poor thing left and right. The owner of the little dog began to scream asking her boyfriend to help her pup as she was terrified. Without thinking, I went after the big dog and he dropped the little guy and ran. Big dog owner came to see what was going on and I (normally very non confrontational but I was livid! ) let the woman have it. I told her until she has her dog trained to stay away from the dog park. The little dog was fine but had some small bleeding. I told them to report it. Gave them my name and number. The Will County Forest preserve did call me for a witness statement. Gave me a number to call if I saw that woman in the park again which I have not. The county was great trying to follow up on it. People need to supervise their dogs at all times.