| I have the same issue but my cats are all 15 pounds and my dog is 6 pounds full grown....but she still goes after them with a vengance. We taught the command "off". We started by teaching it with a treat. You put the treat on the floor and cover it with your hand. In your other hand is the reward treat. You let them see the treat under your hand, when they approach it say off, when they back away give verbal praise and reward treat to eat. Keep repeating until you are able to say off without covering it and they back away. Then we progressed to learning off with other things that were favorites: pens, dryer sheet, slipper. When we mastered that we moved on to cats. The difference now is they are all buddies and wrestle and play, but my oldest one who is 12 gets tired and she still attacks him to play.....that is when we say off and she backs away. Of course if you look away we will very quietly try to aggravate him again & when we turn around she stops immediately. Which means not only did she learn "off" but she learned that her actions were not acceptable (when she was caught anyway!! haha) | 
