That's a good idea. What breed? I normally find mixed breeds the best in training around other animals with the exception of Pyrenees or cattle breeds. Did you also train the horse to equally respect the dog? Often that's not the case.
If so may I ask how? That's one of the reasons I joined. A friend and I will likely share a home out in the sticks and would like peaceful co existence not worried about my two therapy dogs. Advise please?
My dog is a mix, and it's funny that you say you don't use Great Pyrenees often, as he is half Great Pyrenees! lol he's crossed with a Boarder Collie.
I've had him since he was 8 weeks old, and basically, I started bringing him out into the barn, and around the horses as often as I could. My horse LOVES anything small (kids, dogs, cats, etc), so he immediately struck up a liking for the dog. And with time, they both learned to respect each other (there was one incident with a tail that got stepped on, but it was the the hair on the tip, so no real harm occurred, and it was a good learning experience for them both).
Since I was outside so much, I used a longer leash (12 or 16ft) that I looped around my waist and clipped to the dog, so he would learn to follow me, pay attention and respect my space when I'm on the ground. I did it mostly while I was mucking stalls, or doing outside chores that didn't involve the horses. Once he grew up a little, I introduced a shorter leash (6ft), that I looped around my waist, so the dog had to stay right by my side while I was working with the horses (grooming, and leading them mostly).
When I was away from the barn, I worked with a professional trainer to get voice commands down perfectly (Sit, Stay, Come, Speak, Go Home, Lay Down, Heel, etc).
We took him out on his first trail when he was 2.5 years old, with a couple of very laid back, bombproof hack horses. We rode around an area that he knew (about 3km of trail), and brought him back a very happy, tired puppy!
He's 5 now, and still accompanies me on trails. We've also (because of the collie breed in him) got him herding horses now. We only use it in emergencies (horse's get out, etc), but it sure is handy.
Hope this helps!