Hi!
I ride regularly at a place up in St George:
http://ranchzangalisa.free.fr/index2.html
generally we hack out for 2-3 hours on a Sunday afternoon through the woods. He does do lessons too but I've never had one with him and so can't comment on that.
There is the possibility of livery too, which you should find info. about on the website. From what I've seen of the horses there and from the way Andre (the guy who owns the place) is with them, I would say that they are excellently cared for.
If you want to know any more about the place then please let me know - I'll be off up there on Sunday.
I'm pretty sure that livery can also be arranged at
http://www.manege.ch/ which is the riding school in Gimel. The lady there is American. My daughter has had lessons there and it seems very nice. There is also:
http://www.ecuriedesdudes.ch/ which is in Essertines sur Rolle. Have never ridden there so cant say much about it but do have a friend who keeps a horse there.
Hope this is of some help to you, let me know if I can help in any other way and hope you manage to get your horse out here.
emma