I am very Sorry this happened to you. But that is the reason why I don't go to dog parks. We have tried to go but people bring small dogs into the big dog park. To me personally I think a Beagle belongs in the small dog side, I maybe wrong but whatever wrong or right, a lot of greyhounds are not used to being around other breeds if they were just off the track. I take mine to a open field that is open and we go at times other people are not or we will go to grey play groups where all dogs are muzzled but I have seen bad experiences there too, I personally just like to have mine run the yard . I had a bad experience too when I went to the dog park when we first got our greys and a lady brought her dog into the big dog park, it was not as nice though...Please don't be too hard on yourself.....