I can imagine the hours that are used to train these horses.
And you can't really rehearse this circumstance, with real crowd, real crowd noise, and the real tension and excitement in the air.
There is a write up on the USTA(united states trotting assoc.) web site www.ustrotting .com about the riderless horse .
Sgt York is a 9 year old retired standardbred race horse, who is quite used to crowds and distractions. The horses pulling the caisson are warmblood crosses.
Yes many hours are put into training them. and the do several missions (Military weddings and funerals every year.