Susan, I really think endurance asks a lot from out horses. I have done dressage, hunters over low fences, Enghlish pleasure (hunter type) , Westrern pleasure, some cutting on my dressage horse and a gazillion miles of trail riding in the last 44 years. There's nothing quiite as encompassing as endurance riding. I decided last year to devote how ever many rides it took to schooling Hunter. If he got crazy, I just got off and stood in the shade until he relaxed. If you check his AERC record, you can see the slow times and poor placings. I have seen people leading their horses out at the start for the same reason. Any time you spend helping your horse to be less influenced by the chaos around him/her is a good investment.
Confession time: Hunter started the last ride sideways because his traveling companion was going out fast - they were first and BC - and I had no plan for riding that fast. He got over it and had a nice safe ride and was still quick enough to come in 12th. I'd rather he had a nice sane ride than top 10 any time. You'll be just fine. And, as you noted, there's nothing I've ever done on horseback that was more fun. Nancy
