You can lead a 9 ft. tall horse to water, but you can’t make him drink. As I think of it, you can’t make a 9 ft. tall horse do anything he doesn’t want to do. I would not advise mounting a 9 ft. tall horse, not without a saddle the size of a small rowing craft. If you do insist on riding him — which I wouldn't encourage — you’ll need a ladder of some sort, or one of those infernal garden trampolines to launch yourself aboard. It goes without saying, but say it we will: Never look a 9 ft. tall horse, gifted or otherwise, in the gummy choppers. You'll require goodly sustenance — say, carrots the size of a yardstick — to feed the mammoth creature, however, don’t be fooled by his docile nature.
A hungry, 9 ft. tall anything is liable to make a meal out of you. Make a bloody note of it.