Austen, hope you don't mind, but this one is inspired by you and is for everyone out there who is banging their heads in frustration when their horse has thin soles.
Just bear in mind that one of the horses in the sole thickness post had incredibly compromised hooves, but even without boots we had the horse ready for work in just one summer. It can be done. With a bit of patience and ear muffs (to ward off the mites.....).
Let's go back to DETECT.
Diet - every horse is an individual. There are some basic principles which will set you on the right road, but you will need to figure out some of the specific twists and turns of your own horse. Read the posts:
Health food won't hurt your horse, so cut the sugar, molasses, alfalfa, haylage and the wheatfeed. Soak and rinse your hay if you have to. A thin sole is a warning. Ignore it at your horse's peril. Especially if it goes in tandem with a stretched white line.
Some view supplements as the work of the devil, I guess some are. I have to supplement because in the UK our grazing and forage is typically short of copper, zinc and magnesium to name but three. Not all supplements are equal and not all horses do well on the same one. Give it some time, read the labels.
Exercise - a hoof needs to move. Not just plonking about a pasture/paddock/dry lot/stall. But really move. Think about what it has evolved for - 20 miles a day plus all the gymnastics involved in horsey family life.
Many newly deshod hooves just can't cope with real movement to start with. They have been crippled. You know how a broken leg loses muscle tone in a cast? You get the idea. So start with a graduated programme. Boot for exercise if you need to.
Make use of any surfaces you have to test progress, but be respectful and if your horse says no, then no it is. I generally find that thin soled horses do well on very smooth tarmac (black top). Even 20 minutes walking 3 X week will help build sole. If you don't have access to this, then concrete can be substituted, but tends to be more challenging, so it will take more sessions of shorter, gentler walks. Don't trot until your horse can step on stones on the tarmac in walk without flinching.
Need to canter jump and let rip? By all means, if your horse can otherwise cope, but do your canter work in boots, or in the school. I am not convinced thin soled horses should be jumping and I am not convinced it is totally safe to jump in boots unless they are a good brand well fitted.
Time - to build a healthy hoof takes time. Some take longer than others. Footiness post dietary problems can be resolved within days/weeks. Thin soles take a bit more work to grow the material required and work it into a tough, dense structure. It also takes time to figure out the right diet for your horse. It takes time for the hoof to respond to the change in diet and work load. Give it that time. Take photos weekly, you will be surprised by the results, I can't promise they will always be happy surprises.
Environment - a hoof is responsive to the environment in which it lives. But that doesn't have to be a completely limiting factor. I used to keep my gang on a field which was very wet (complete with spring and marsh grass). But they got out most days to do road work and responded very well to this. I have clients whose horses are living in very 'unhelpful' environments, but again they thrive if they get to do the work. The ones that don't do so well usually have dietary issues. Diet and exercise count for more in my book, although a great environment is really really helpful, a not so good one doesn't have to be the end of the world.
Communication - a two way process. Unfortunately the BHS, parelli and others seem intent on making it one way. I have been very firmly taught by a succession of incredibly bright horses that I will get on much better if I listen to them (which includes observation) and respect what they are trying to tell me. It is not easy, I am a numpty, but my girls are patient and keep on trying so long as they feel I am trying. In my mind there is nothing so sad as the horse with the blank/far away look; they have given up because no one listens. A bit like the kid who doesn't bother crying any more.
Sometimes the communication is very subtle. Grace started off with just a tiny tiny lip wrinkle. Now we have a full range, but it took a while. Also observe posture, ears, hoof signs, etc etc, it all adds up. They can have some sort of pain from their guts without it being full blown colic and all you will see is a swishy tail maybe, or resistance to saddling or frequent wood chewing. Horses are co-operative by nature, if your horse isn't then find the reason why.
And if your horse is footy, find out why; check diet, but don't forget the obvious (like stones stuck in the foot).
Trim - boy are there some bad ones out there, but unless really dramatically awful, or regularly repeated, the damage can usually be grown out. The best trim in the world won't 'cure' a thin sole, at least not overnight. But a good trimmer can faciliate the hoof on its way to health and they should be able to advise you how you can help, without resorting to iron.