Is your horse fed in a manger or hay net above their withers? This builds muscle under the neck, making horses look ewe necked, so, if you do feed higher than his withers, start feeding in a trough on the ground. Some people say unrefined coconut oil can help.. Also, trotting up and down hills and doing trot poles. Teaching your horse to be on the bit while backing up can work wonders.
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown