So sorry to hear this. Did the owner say it was a Pit Bull? Or an American Bulldog? American Bulldogs are quite tall, like Boxers. Pit Bulls seem to be called American Staffordshire Terriers now in order to get round the illegality of owning them here. I remember several years ago that there were two men who owned an American Bulldog they couldn't control walking in Peckham Rye Park. From what I recall, the dog savaged at least two other dogs, and the owners were tracked down and the dog was confiscated. Maybe you could ask the park warden for help.