Apparently, my horse (Snafu) and boss's horse (Raja) were in the indoor arena, and eating some hay scraps, minding their own business. The girl who was working today brought her two dogs, a rottweiler and a daschund. I guess the daschund found a way to slip into the arena with the horses. (Who are both around 17hh. Although, I'm sure ponies are fully capable.) He got too close to Snafu's tail/hind end. Snafu kicked, and broke the dog's back.
The girl is upset, and blaming me. I, at the time, was at school completely unaware. I think she shouldn't have let her dogs run loose in a stable. There would be no way that daschund could have gotten away quick enough on those short little legs. Snafu, has a good reason to be defensive. He was once attacked by a pitbull who bit his nose and hung on while he thrashed around. Not exactly a good dog experience. I feel horrible that her dog was killed, but it's not my fault or Snafus.