Here is my trick and it works on fast running dogs, kids playing etc. I set my camera to one small focus point and it put the spot wherei want the subject to be in the frame. I give lots of distance and let the animal run to me. I also use a shallow death of field in case the background is less than ideal. Then as the animal closes in I put that spot focus on its eye/head as besti can shooting in bursts. With practice it works for me.