If the dog moves from the sit/stay, do not run up to correct him. Slowly walk back and heel him into the original position from which he moved. Place him back into a “sit”, and correct him from moving by firmly snapping upward, repeating the word, “stay”.
Always give the “stay” command before leaving your dog. Make sure you do not say the command as you are leaving. The dog will want to start to move with you in the heel position, if he is not told to “stay” before you begin to move.
Increase the “hardness” of the correction as needed.
Do not raise your voice.
PRAISE your dog when she responds to the first command that is given!!