Hi there Becky. I drive ADS style so we don't tend to use appliances or anything artificial to get our horses into a frame. That's one reason I drive ADS, actually. But I know you're looking at a different discipline so I'll tailor my answers accordingly.
1. Is a bitting harness essential in the driving training of a horse? I only ask because if it is not, I would rather not invest $200 or so dollars in something I'm only going to be using a couple of times.
Nope, I'm with everyone else- use your harness saddle and ground-drive the horse.
2. My harness does not come with a running martingle but in the books and video I've looked at, they all talk about it and about how it helps a green horse establish his head set and gives you better control. Should I order one?
Running martingales are pretty specific to the breed ring and to me often do not seem to be adjusted to actually do anything. The only way I can see that they would give you more control is to prevent the horse from doing what comes naturally when he is stressed and his head is being held way up in the air and bolting. If you train him carefully and only tighten the check as the horse is ready to carry himself that high, then you shouldn't have any problem. They don't do any harm but they're mostly decoration unless you have
really checked your horse up.
3. Splint boots- I think I'm going to order some but do you/did you guys find them useful/preventative?
Ya know, I've always been more of an au natural person when it comes to my horses' legs. I had Arabs and they were always very surefooted and quick on their feet so I never had any problems with clipping or slipping or overreaching. The only time I used splint boots was in a local fun reining competition where they required that you wear them. When Spyder bowed a tendon in the pasture at 27 or 28 years old I got him some Sports Medicine boots at the vet's recommendation to help support his leg, but he hasn't used them since he healed.
Most horses wear protective gear on marathon at a CDE but the minis generally don't because it's hard to find splint boots that fit well enough to not slip around. They have some cute sports medicine boots for the minis now but I'm not sure how supportive they really are as far as the suspensory ligament. I still want a pair because at least they fit better and will protect the whole cannon from impacts. I worry more about my horse bouncing off an obstacle than off himself! LOL.
In any size horse using boots depends on what you do with the horse and what kind of footing you have. If you do fast spins, stops, whirling, etc., you should definitely use boots. Otherwise I prefer them to go bare so that the tendons strengthen themselves. Constant support means the structures of the leg never toughen up and if you ever take the boots off....uh-oh! Besides, with a barefoot horse they aren't as likely to injure themselves if they clip a hoof and the sting will teach a klutzy young horse to be more careful.
: The only time I'd use boots without hesitation was if I was driving a team. One horse cannot be expected to know where the legs of another are and accidents would be all too easy in fast turns. I paired them, it's my responsibility to protect them.
Leia