"I can't get him to stop unless I circle him. I can't get him to halt when he does these things so I can't make quick corrections. This situation occurs mostly when he is schooling with other horses.I have no idea why. I ride him with others all of the time. Other times he is respectful but I still have to half halt like 20 times to keep him even paced. He basically ignored me unless he feels like listening."
I start young horses for a multitude of events, and have started a lot of event horses. You have answered your own question, in a way. Your young horses is not broke. You should be able to stop him when you need to, and be able to back up, anytime, anywhere, and do it in a plain ring snaffle, or you should not continue jumping until you can. That is what your flat work is supposed to accomplish, control, among other things. Sounds to me that he needs a better foundation. If you are all ready using a 3 ring, and you still cannot stop him, you are headed in the wrong direction.
Plus--Ann Kursinski exercises, which I also call "blue in the face exercises."
I usually do this with show jumping but you can adapt it to XC!
1. Two fences at least 7 strides apart. Trot the first one, halt, back, trot the second one, halt, back.
2. Trot the first fence, walk, trot the second fence, halt.
3. Trot the first fence, trot the second fence, halt if needed.
4. Canter the first fence, trot the second one.
Throw in halts or backing where needed. This works with many, many horses.
Ive tried the pelham a couple of times and it works very well. I decided to go with a happy mouth version. He didn't like the metal straight bar or the rubber straight bar so I bought a jointed happy mouth pelham.