If you want some further basic dressage training to help you with him (I did read that the one dressage lesson did help), go to USDF’s website and locate their list of instructors, and start calling them. There are plenty that will travel to your location instead of you travelling to theirs. The listing is broken down by regions. If that is an option for you . . . even a lesson once a month will give you things to work on with him that will help you both. One of the other boarders at the barn I am at has a mustang mare that has two speeds . . . fast and faster . . . since beginning some dressage lessons, the mare has actually started learning to relax and slow down. Hopefully, this will carry over to the show ring, since that is a different environment.
I have a young horse (3 year-old) that is similar in many ways, but is actually not an Arabian (we thought he was part Arab until I got the DNA testing results back from Texas A & M . . .he’s part Hackney Pony . . .). He spooks at everything I don’t expect him to, doesn’t spook at things I think he will, was mishandled before I got him at 2 1/2, and has been a challenge from day one, but so worth it in the end. He has not been backed yet, due to his reactive nature. I have been taking things very slowly with him.
Your boy has had more years to get set in his ways than my boy has, but it does take time to convince them that what you are trying to teach them makes sense! If you have a tendency to be nervous, they do pick up on that. My confidence has increased the more I have been working with my boy, and now my mare (Appendix QH who is under saddle and heading for her first dressage show the end of July), which is showing through in how he is responding. I am more confident, so he is picking up on it.
SmartCalm Ultra is one thing that has helped with my little livewire, but I will have to change to the basic SmartCalm before I show him in any USDF shows. Neither dulls a horse out in the least, but it doesn’t really sound like your guy needs that, as it is just at shows that he reverts back to the race horse. It’s the larger group and possibly the added stimulus of the loudspeaker, the crowd and the extra activity that is bringing that out in him. There are some other things that may have been mentioned that could possibly be used a time or two until he really figures it out. Best of luck to you with him, and I hope you get to really enjoy a show on him and have him stop racing the other horses!