You really have to be all over them all of the time. Icing, packing, rubbing, hosing - lot's of cross training and long slow warm up and cool downs. I believe you can ride your horse to better overall state of well being by being the hores physical fitness and PT coach. Make a calendar and plot out the horses work schedule.
Make sure they are in a safe stall/paddock/pasture with no nails, sharp objects, or really anything that could easily cause an injury. Use polo wraps or splint boots when riding, and you can even use certain wraps in the pasture.