I recently started riding this lovely horse who has beautiful gaits and is very responsive, but has a tendency to hold his head quite high and sometimes even horizontal to the ground. This is most prominent when he is hot and sensitive. During canter, he will round up more; it is the most problematic in trot. Any attempts to get him to lower his head with half halts only causes him to trot faster and snatch at the bit, and gentler half halts will not produce any effect.
Please help. He's quite a good horse with nice conformation and high potential.