Losing the wall in the background is also a good idea, as it is quite distracting sitting up at the op there. If I were doing this I would also hope to remember to clean up the area of distracting items, such as the old brown leaf in the first shot, but my memory as it is I would probably fail on that. As Frank says, I would go with a much slower shutter speed and pan, that will give a much better sense of speed for little dogs like this one. Freezing the action for a large dog can work, since you have a much greater separation from the subject to the ground, emphasizing the action. For that to work with a little one you would need for it to be jumping off something to get that required mid air effect. Since you want the maximum of background blur from the pan, I would try to get as close as possible to the dog, without introducing perspective distortion, so that the angular speed is as high as possible. So I would only be considering using something in the normal focal length range. Although a longer focal length would work really well from a DoF point, and the added distance would introduce a pleasing flattening of perspective you end up losing the angular speed, unless the dog runs really quickly.
Alan