I have a three year old forester
Whenever she played up when i was walking her out, i would make her stand still for a good couple of minutes then try again, I also had a pressure halter on her which helped a lot.
Make sure you give him lots of praise when he does what you wanted, treats like polos, etc.
I always used to take Lilly out on her own too so i wouldnt get any problems if i were to take her away from another horse, Which seems to have worked as i can ride her out on her own and she is just the same if shes with another horse.
Anyway, so yeah, pressure halter and patience