I Had a gelding who would NOT stand still for mounting, it was awful! The former owner told me he did that, but I still didn't expect how much of a PITA he'd be about it, I did a lot of work with him on that. When I'd go to even step towards him, he'd start moving away or circling, so I'd force him to keep doing it, until he finally decided to stand, at which point I'd see if he'd stand for me to get on, and he usually wouldn't

, so I'd send him around and around again. Sometimes it took about 15 minutes to get on, but I refused to get on until he stood still, and made him realize that actually standing still was a lot less work for him.
If it's not stopped, it's omething that will get worse, and become dangerous. Getting someone to just hold the horse while a person mounts isn't really the answer either, it's basically just preventing him from doing it that time, but doesn't actually teach him anything, and there won't always be someone there. Just thought I'd mention that, since I've seen people take that approach too, and it definetly doesn't fix things.
Glad to hear things are improving with Blue Jay, hope you can get through this issue and things just get better and better
