I actually have the same problem with Billy. Most of the tracks and my road are brash and he is footy on them. He picks his way sometimes tripping. Hes happy on the hard tarmac so it's just the stones.
I use some of my golden hoof sheep foot dip. Helps to kill off nasties so any thrush and bacteria and hards the hoof. I dont do it regularly enough which is why mine is footy. Also with the wet dews in the morning the feet are softened over night alot more than they were in the summer months.
You could invest in some boots. But I've read there no good on hairy cobs. So it counts me out.
I'm going to invest in one of those mats that you soak and I can add the foot dip too, so I can have it in the gateway on the floor in side my tack up area, so they have to walk over it when they come in. Billy's a bit funny with his feet so trying to get him to put his feet in the bucket to soak for a minute is impossible which is why I'm not treating him regularly. I have painted the foot dip on his soles but I really dont think the feet get soaked long enough. Certainly with the sheep any that I put through the foot bath that just walk through still have thrush a few days later. Where as the ones that walk though and let stand in for a minute or two, the thrush is killed quicker. The mats are quite expensive and I haven't seen one yet that I think will be suitable for the horse, so I've been racking my brains as to whether I have anything at home that could work.