If you're unable to keep your horse at home you'll have to search for a boarding facility that can provide optimum care. Since stables are not overseen by a governing board you can't rely on an official grading system or a four-star rating. Instead you have to conduct your own research. That includes asking for referrals at local feed stores and veterinary clinics. But nothing beats investigating a facility firsthand.
When you visit a prospective boarding stable, survey the overall condition of the horses. Are they generally in good flesh? Do they have continuous access to fresh water? Are their corrals and stalls cleaned of manure? Is each horse provided with shade and shelter? Are the fences and gates kept in good repair, free of broken boards, sharp corners and rusty nails?
Ask to speak with the barn manager or on-site trainer. Get specifics about the feeding program. Many public boarding stables have a one-flake-serves-all feeding regimen that doesn't account for the wide range in horses' dietary and nutritional needs. There should be an ala carte option if a horse needs additional feed or supplements to maintain its condition.
Finally, a well-run boarding stable establishes protocol for behavior that enhances the welfare of the horses. There should be posted safety rules as well as a palpable atmosphere of respect for good horsekeeping skills. And because of the communal aspects of a boarding stable, all of the resident horses should be maintained on a regular schedule of vaccines and de-worming. That will help prevent the spreading of contagious diseases and parasites from horse to horse. Ultimately, it's worth seeking out a well-run boarding stable that promotes responsible horse care and makes a conscientious effort to provide a safe environment. Such a facility will probably make a perfect home for your horse.