There's a bit of interesting history with Dawn and backing. When we first got Dawn, when you asked her to back, she would rear instead. It turned out she really didn't know what to do with her feet and the energy she had, and when we put pressure on her mouth, she didn't understand that we wanted her feet to move backwards and the energy had no where to go but up. We trained her to back by working with her on the ground. It seems to me that a number of behaviors like rearing and bucking often reflect the redirection of energy upwards by horses who have no other place to put it, particularly when they don't understand how to soften to the bit and therefore the energy is piling up in front, so to speak.
After we worked on our backing for a while, we tried an exercise that I like a lot - it's really an exercise in how subtly I can communicate and how attentive I can be to the horse and to giving a release the instant I get the response I want. I call it "one step at a time". The objective is to stand where you can see all of your horse's feet - either facing the horse or with your body turned slightly toward the horse, and then ask the horse to walk forward, but to move only one foot at a time, stopping after each foot moves. The key is in giving a release the instant the foot starts to move - otherwise you get two or more feet to move. It's fun to see if you can give a release for something even smaller such as a lean in the direction of moving but where the foot doesn't leave the ground at all. For me, this requires intense concentration, and for the horse, paying close attention to what I am doing. Dawn thought this was a fun game, although we took some rest breaks to walk around or do our backing again to mix things up.
Then I had intended to work with her on various backing exercises involving a pole - such as backing straight next to a pole, backing over a pole, etc. I don't like to use PVC poles for this, as they're too likely to roll, particularly if stepped on, which could startle or even injure the horse. So Dawn and I went to the corner of the ring to drag out a nice, heavy, octagonal wooden pole. Once we had the pole out, I walked her across it a few times and it quickly became clear that we wouldn't be backing over the pole today. Dawn clearly was anxious about the pole. Although she is a physically capable jumper, Dawn is very nervous about anything resembling a jump - apparently even poles - probably due to a very ugly incident from her past involving a set of jumps that Dawn was confused by, an angry and impatient trainer, a lunge whip and my then 12 year old daughter. This incident was the final straw that led us to seek out other, non-coercive, ways of working with horses and also led to our immediate relocation to our current barn.
In any event, it was clear that the issue to be worked on first was Dawn's simple nervousness over crossing the pole - she wanted to avoid it, she wanted to rush over it - rushing being her usual response to being nervous. So we worked for a while on walking slowly over the pole in a relaxed frame - we did a lot of head-down cues to get her to stretch and relax. That went pretty well, so we called it a day. I was particularly pleased how well she did, since I've never worked her in the morning before - only after bring-in time - but Lily and Maisie were nearby so that probably helped.
After that, things got more interesting. I led Dawn by the small grass paddock, where Noble and Fritz were at the time, and took her up to the dry lot paddock where Maisie was, thinking that Maisie might like some company. Lily had been waiting for the farrier in a stall, and was bellowing and nickering - she's coming into heat and is very demonstrative. Dawn is also coming into heat, but she walked by the geldings on the far side of the aisle without a problem. Once I put her into Maisie's paddock, she started "demonstrating" - showing the geldings that she was interested in their existence but that she would kill them if they tried to get any closer - bellowing, striking, head-flinging, bucking, etc. Ah, the joys of mares in heat! When the farrier was ready for Dawn, I took her out of the paddock to lead her back to the barn (which would have involved passing the geldings) and she went berserk - all four feet left the ground in different directions, accompanied by screaming and tail-lashing. I gave her a sharp correction with the halter to try to get her attention (this sort of thing and threatening to bite or kick another horse while on the lead gets a strong correction from me), and managed to get her back in the dry-lot paddock.
I then removed the offending geldings to the barn and came back to try again. As I led her out of the paddock, the fuse blew again - I think it took her a few moments to realize the geldings weren't there anymore and perhaps she was aggravated by having been in the dry lot where she doesn't usually go - but I didn't care about that, I cared about not being struck or trampled. So I did a self-preservation technique involving keeping the berserk horse on one side of a fence and my body on the other, holding the lead over the top of the fence. I went back inside the paddock and led Dawn down the fence line, with her on the outside and me on the inside. She continued to scream, buck, kick and strike. This went on for a few minutes and then she stopped. It was like a switch was turned on and then off. She has never before done this with me on the lead line in the 8 years we've had her - and I hope it was an aberration and never happens again. She led down to the barn without incident on a loose lead and was a perfect lady for the farrier, as she always is. I turned her out in the small grass paddock afterwards with Lily - no problem, but then again there weren't any geldings around.