Ok great information. Based upon information provided so far it sounds like it might be something as simple as he has bruised his sole(s). Statistically 95% or greater of lameness in the horse occurs in below the fetlock joint. Given the history that you told me so far if he was used to having shoes on his back and he went for a vigorous ride without shoes it would predispose him to bruising his sole because each time he steps his outer hoof wall is able to expand more than it would be than when it was restricted by a shoe causing the frog to impact the ground farther which predisposes them to bruising. While this "bruising" sounds benign and simple it could lead to a subsolar abscess, a.k.a. a foot abscess. If you want to look for a bruise, the best place to look is about 1-2 cm just in front of the tip of the frog. If he has white soled feet, bruising is much easier to see.
1. Leave his shoes on.
2. Stall rest 24-48 hours.
3. After the initial period of stall rest he can be and walked on a soft footing for 10-15 min. at a time if needed. If Homer is content staying in a stall, then extending the stall rest up to one week would be great.
4. During this period of stall rest I want you to add 2-3 cups of Epsom salts to warm water and a rubber ( not plastic) feed bucket or other similar container and soak his feet for 15 min. at least once a day, ideally twice a day. The best way to add Epsom salts to water is to pick the bucket that he will stand in first, fill it with warm water, then add enough Epsom salts to the point that the Epsom salts no longer readily dissolve.
What the Epsom salts will do is help soften the hoof capsule walls so we can increase blood flow to the foot. Blood is good. Blood = immune system. Immune system = healing.
5. If you have a Phenylbutazone paste, powder, or pills let me know.