I suppose if I have to ask if its safe in a driving thread, the answer by default should be no? 
Right now Ive been teaching my 9 yo TB to drive. He is lazy, stoic, clever and when uncertain what to do, just stops and stands still and waits for you to help him, no bolting and reactivity, just pretty chill-so seemingly a reasonable horse to teach to drive. We have done long lining, harness wearing and he just started pulling a drag around and seems quite intrigued by everything and is very agreeable.
The other horse I have is an 18 yo welsh pony/cob cross. She is not fearful, but is a fiery hellion to the other horses. She was given to me for free as she is ruined under saddle and wouldnt take for breeding. But she is a beautiful mover.
In hand, her stable manners are good. Initially she actually seemed fearful of me, like she was waiting on me to smack her, but that abated quickly. While lunging, she tosses her head around like a little stallion and puts on quite the show, but listens well once corrected. She responds best to direct, but subtle, refined, precise correction. She can be resistant a bit, but has never shown any sign of aggression to humans, even when I had to treat a large cut she got and hoof abcesses.
Working with her, She initially would act out, then tense up in fear. My assumption and from learning a bit about the previous rider, is that she is by nature a challenging, strong willed very dominant animal who will test you. The previous rider was a rather dramatic person, who then would respond in an overly loud, aggressive way to correct the mare, then hold a grudge. The mare, by nature, would continue to challenge her, and things would escalate. Eventually she was used as a riding school pony but was so bad, she was put to pasture.
Ive tried her under saddle a few times and she has every possible method to prevent being ridden-its a very predictable catalog of evasive techniques. Balking, cow hops, not standing still etc. Each can be overcome, and we work through them, but what is most obvious is that she HATES the idea of being ridden. Her tail lashes frantically each time she is mounted and she becomes very apprehensive and unhappy. I figure 18 years of being ridden badly likely is the cause as a vet previously owned her and didnt call out health issues.
I know the general rule is that driving should not be the solution for the horse that cant be ridden, but my thought was that maybe she just needs to try something that hasnt made her miserable in the past. She is calm, energetic, bold, smart, sensitive and responsive, as well as challenging and willful. She is not bolty, fearful, doesnt shy, listens well once corrected, and is not aggressive or ugly to people. Oddly-she wants to be good, once she understands what good is and responds well to subtle praise.
Red flags, concerns, suggestions about training her to drive?
