Please try and hack him in the fields rather than on the road. Keep him at a walk and as you are walking ask him to bend and do different things. You can make small circles or halt and make him stand for a minute. Vary the routine so that he does not know what to expect. If you can have another horse with you it is better.
Horses are happier in groups.
Arrange with the other rider that all you are going to do is walk. When you are able to take him out and have him behave then you can try riding on the roads again. As before though keep it at a walk until he learns that he still needs to do as he is asked when on a ride out of the ring.