The short answer is that this horse has been conditioned to only respond to the grossest cue for forward. You can retrain him to respond to a very light cue for forward, but it would mean never listening to his current owner, because she is the one who taught him the wrong thing.
Horses learn by release of pressure. If you ask with the lightest cue and there is ANY response, reward by ceasing to cue. This is how you gradually teach the horse how to obtain the quickest reward -- by responding quickly to the lightest cue. With a horse with the ingrained habits of this one, you are going to have to re-teach him from the beginning. It will take patience and attention.
Thinking that 'you can't let him get away with anything' is not a useful way to approach this issue. The best attitude here is "let me help you learn how to do this differently".
Example. When I got my filly she did not know how to go forward on cue. She would just stand there wondering. I was shown how to apply pressure (in the very beginning, just rhythmically thumping her sides with my heels -- not accelerating, not punitively, just thumping moderately) until she took a step forward. One step! Then I quit thumping, that instant. Let her breath and think about it. Then start the thumping again. Thump when standing, quit when stepping forward. Very quickly, she learned how to avoid the thumping! This is the basic idea. From there, we refined it, always aiming for the lightest possible cue and the quickest reward I could give her. Timing is of paramount importance, otherwise they won't know what they did to make the pressure stop.
Always remember than horses want to be in harmony with their environment, which includes you. They want to know how to behave to avoid jarring and confusion and ugliness. If they consistently don't avoid it, it is because they don't know how.
Horses learn by release of pressure. If you ask with the lightest cue and there is ANY response, reward by ceasing to cue. This is how you gradually teach the horse how to obtain the quickest reward -- by responding quickly to the lightest cue. With a horse with the ingrained habits of this one, you are going to have to re-teach him from the beginning. It will take patience and attention.
Thinking that 'you can't let him get away with anything' is not a useful way to approach this issue. The best attitude here is "let me help you learn how to do this differently".
Example. When I got my filly she did not know how to go forward on cue. She would just stand there wondering. I was shown how to apply pressure (in the very beginning, just rhythmically thumping her sides with my heels -- not accelerating, not punitively, just thumping moderately) until she took a step forward. One step! Then I quit thumping, that instant. Let her breath and think about it. Then start the thumping again. Thump when standing, quit when stepping forward. Very quickly, she learned how to avoid the thumping! This is the basic idea. From there, we refined it, always aiming for the lightest possible cue and the quickest reward I could give her. Timing is of paramount importance, otherwise they won't know what they did to make the pressure stop.
Always remember than horses want to be in harmony with their environment, which includes you. They want to know how to behave to avoid jarring and confusion and ugliness. If they consistently don't avoid it, it is because they don't know how.
