Respectfully Krazy, you showed us a pretty bad eg. above with some alarming looking problems. You said it was from today(tho then you say the horse is unshod), 2 months after the last pics, which while can't tell much from that angle, look better than the 'today' one in a number of ways. But of course, Spirit, don't forget we're only getting a very small part of the whole picture & IME there could still be a number of factors that mean it may not be the farrier's fault the hooves have got into that state.
...Now back to OP.
I will look into magnesium for him. I'll do some research myself and also contact my local vet to see if it is something that might be needed in my area.
Good move. I don't believe it's a good idea to give supps without good reason, just because someone(or some lable, advertisement...) said. Your vet may or may not know much about nutrition & specific studies into Mg though, so don't just stop there.
Look up 'magnesium for horses' for a start. There are also a lot of human studies that have been done lately, which have been the basis of horse case studies into it.
However, I will forgo the epoxy and try treating for fungus first. What products do you guys like?
Yeah, epoxy won't help aside from looks & you don't want to plug it up with anything unless you can guarrantee keeping the bugs out, because that will just create a nicer environment for them. 'WLD' can be fungal or bacterial, so a broad spectrum treatment is the best. If it's only in the wall, virtually anything antiseptic - I tend to use a weak peroxide wash first, then a t-tree & salt & copper mix, heavier chems if that doesn't cut it - but if it goes deep into the laminae or worse, I'd be careful not to overuse anything too harsh, as you don't want to damage the live tissue with heavy chemicals. In that case, believe it or not, raw honey(particularly types such as Manuka) is a really good but non-damaging antiseptic.
I may try riding him in boots again (I'm taking a hoof care and trimming course at our college this spring) this summer if I can get his feet in a condition that I think they can handle it. Just don't want to spent over $300 in boots just to have them sit on a shelf.
There are many online lists, registers, forums, etc for second hand boots these days & esp if your horse is a common sort of hoof size, you'll probably find what you want for secondhand prices. Particularly as your horse has a lot of flaring, so the boots that fit him now will be too big down the track when they become healthy.
His feet should 'handle' riding in boots much better than being shod IME. But how is he bare in the paddock? If he suffers bare just on what he lives on, his feet sound very unhealthy & in need of TLC. While some boots can
be used full time for rehab, they're often not the best choice if the horse requires that sort of intensive care & cost is one of the prohibitive factors - if a horse is that bad, they usually also need pads & most riding boots aren't suitable, meaning different boots(RX Therapies for eg) are needed for rehab as for riding. In that case, hoof casting may be a better 'do it yourself' option, but Trinity is the one with experience in that - I'm still learning(tho Trinity, I have been casting my own horses recently, in different ways, with & without padding, etc.)
My main concern with casting is that as with sealing up cracks, the risk of infections getting worse because of the sealed environment it creates. Unlike boots it can be impractical to remove/redo the casting daily to effectively treat/clean/dry the hooves, but I have been experimenting with removing the casting & reusing same, just duct taping it back on around the top. Seems this may be the way around the impracticality of the single use.