Question: If I don't want to ride that day can someone else ride my horse for me.

Answer: ONLY if they are a Rider Member. The ONLY people that can be mounted on a horse at the training ground are "Rider members" and those who have pre-purchased a "Day Pass".

Even if they are just warming up my horse, Doing a pre-purchase ride, Schooling my horse, Just hacking, really I won't jump or use an arena, the answer is NO. 

"Rider members" and those who have pre-purchased a "Day Pass" are the ONLY people allowed to be mounted in the training ground.