This is one of the reasons I keep my distance from shoes. They fall off, cause hoof wall damage, tendon damage, allow the horse to not correctly feel lower limb, and don't allow the horse to correctly wear his/her hoof. As a natural horse caretaker/guru, my solution: Easy Boots.
Why spend 100 dollars for shoes when you can pay 150 for a pair of boots that'll last you a season or more.
My experiences have led me to love the easy boot glove the best, it's very low profile and stays on fabulous. I also do CTR's and endurance racing and was devastated that I would have to use glue ons because of the 'nothing above the coronary band' rule, but THANKFULLY, they have changed the rules
now allowing these types of boots. You can look at the new rules on the ECTRA website.
Please take a moment to consider this alternative, it will save you and your horse! The Easyboot Glove | The Ultimate Horse Hoof Boot | EasyCare Inc.
As for riding with a missing shoe, heck I wouldn't ride a horse with all 4 shoes :P