To use his hind quarters? He is very unbalanced and He doesn't use is quarters and push his legs underneath him. He pulls himself forward with his front legs it seems. Would regular lunging cure this?
Mine it quite similar as he is built slightly downhill.
I do lunge him a lot so he finds his own balance without any interference and when he is ridden or on the lunge I do a lot of transition work to get his back end working more which lightens his forhand and stops him from pulling himself along with his front legs.
others will have others suggestions I am sure but all I will say is, transitions, transition, transitions!
I would say transition help this alot. So do 10 strides of trot, walk, then nine strides of trot, walk etc etc. But I am sure the more dressage competent on here will have some better advice.
Put your leg on, and keep an even contact and he should soften. Start by widening your hands and asking for a longer, more relaxed frame - at the mo, he looks hollow - as said above. You want him rounding over her back and engaging the muscles from behind.
It will make it easier to get a good outline after you have worked him long and low as his back muscles will be well stretched and he will have warmed up. If he has just come back from work, I would just want his long a low for a bit and not ask too much for a while. Just remember, you want head low, but his nose shouln't stick out too much. Make sure he is going forwards from behind and tracking up and it should come together well.
As said above, transitions help get him off the forehand and tracking up. My pony was also similar. I imagined he was a tube of toothpaste (bear with me here!). So, have a good steady contactand hold it. As you do this squeeze with your legs so your horse is propelling himself with his hind legs. As he does this, he should accept the contact and engage the muscles, from his hind to the top of his neck.
Toothpast theory = you squeeze, and the toothpaste works it way up the tube. This is like squeezing with the legs and the muscles engage right from the end to the top and then when the toothpaste finally comes out, it is when the horse acceots the contact. In short it comes from behind
I find trot/halt transitions help..ask your horse to trot with a good even rythm and then ask him to halt at a specific letter in the school, but work toward the halt transition by counting the strides by feeling the movements of his hind legs if that makes sense, so he halts properly and when you ask him to rather than just stopping. Halt for 5 seconds then trot again withot walk in between if possible.
But only do this when you've already warmed up properly on a loose contact, when he can do this nicely and he's lifted off the forehand try walk/canter transitions to get him to focus more.