A few years ago, in a senior moment, I agreed to take two New Forest mares that had run on the Forest all their lives and never been touched. These ponies are as near to Mustangs as you get, but often smaller (around 13- 14hh). These mares came off the horsebox in a pair, they were herded through my series of yards with all the gate wide, straight onto the bottom filed- which is three and a half acres, spilt up into three to allow all field access to the river. The fences are stock fencing and again, all gates were left open (except the ones leading to the top field) so they were isolated on the river fields. The fences never even gave them pause they went straight through them as if they were not there, at a trot. They flattened three fences in as many minutes but were still held by the river and a natural fence line of trees- which they could see and understand. Once they had been with me about a week the started to understand what fences were for, which is when we found out how well they could jump!!!
In the end I passed them onto a friend who had a bull pen. The older mare was sin foal so, since they had "quarantined" with me he put her out with his mares and left her to think about it. I believe she foaled fine and is still five years later, thinking it over!! The younger mare they put in the bull pen and isolated her form equine contact. A fair amount of firm but gently handling went on, in spite of her best efforts to escape.
Eventually she did quieten down- she was only three, we then found out, and she was eventually saddle trained. I believe she was a good pony under saddle.
The older mare is still trying to decide whether or not she likes people, but she is a good broodmare and has nice foals, so she is OK there, thank goodness.
The older mare will never come round, is my gut feeling. They may be able to halter train her- at present they just run her into a crush for her yearly jabs and checks, and only worm her in feed (which she took over a year to learn to eat).
These NF ponies have actually seen people as the New Forest gets a lot of tourists and campers, hikers and riders. They are not nearly as secluded as Mustangs.
I have seen mares over twenty go through the yearly drifts for pennies- I do understand this is no longer allowed but someone was trying to abandon a pen of colt foals and the asking price in the ring was 50c!!!
Sometimes a horse really is better off dead- so long as the death is painless and quick.
The thing that really really annoys me is people trying to make a bit of money out of it!!