Building strong hooves
While researching this I came across a brief dating way back. Zenophon stated that horses should have an area where they frequent to be filled with hand sized stones contained in an iron frame to prevent them from scattering. With clay I think a good layer or two of landscape fabric would be a good idea to to prevent the rocks from being buried. I have carted sand from the road after the grader has gone by and spread the course sand and small stones on a frequently used path going up a hill, about a 20' long strip.