It is because of shots like this that I started following the dog with my lens keeping the dog in focus at all times. It is the consistant capture of the unexpected shots that people remember you as a great agility photographer. I find it easier to follow the dog with my right eye in the viewfinder and my left eye open, watching the event. This allows me to see the unexpected starting to happen and gives me some lead time to get the shot. I still miss them from time to time, but not very often.