Turning to the collective knowledge of COTH for some ideas…
Horse is a 27 year old Morgan. Had a bit of an all-around show career earlier in life, and is now retired as a trail horse with an intermediate adult amateur rider. Rider is comfortable w-t-c, but has confessed the horse scares her when cantering on the trail.
Horse is HOT and strong, and always has been (even when in a full-time program). His favourite tactics are curling to evade the bit, or pulling to unseat the rider. He is a handful even for an experienced rider, but was previously ok in a pelham with two reins.
Current rider is not comfortable with two reins. She has soft hands, and just wants something that she knows she can stop him in when needed (i.e. when he gets strong out cantering on the trail), but doesn’t need the strength all the time. She’s not the type to punish with a bit.
We have tried the pelham with converters, a waterford D ring, and a slow twist D ring. The pelham caused a lot of fussing and head tossing, as did the slow twist. The waterford has fixed the head tossing, but doesn’t have enough to stop him when he gets going.
Looking for some suggestions here, including possible martingale or other suggestions. Yes, the answer is probably to go back to ground work and lessons, but the farm only has arena access a few months of the year due to weather, and there is no on-site trainer or coach. Horse has excellent ground manners, and is good for the rider in the arena, but those features don’t seem to translate out in open fields with other horses. I just want the rider to feel safe on the horse, and be able to enjoy him when out trail riding for whatever time he has left.
Edited: Not concerned about the set-up being show legal for any discipline, as the horse is retired from showing.