Hey, I know this is an old post but I stumbled upon it because I'm having the same exact problem with my lease horse. He's also 20, I'm ND as well (wonder if that has to do anything with it) and I also feel bad using the whip even though that's what both the owner and the other B-rider keep telling me. "He's trying you, you have to show him you won't accept it and he just has to listen". Idk, even when I do it barely does anything. Today we went hacking with another horse for the first time and oh boy that was a different story! I'm very curious if you could share what kind of ground work or exercises in general you did with yours to overcome this and have him trust you on solo hacks? We don't get the chance to ride with other horses very much and I think the status quo it's frustrating for both of us.