You can stop your horse from tuning you out by keeping him engaged with you. You do that by moving his feet forwards, backwards, left and right. When you start a training session, you should have a set plan about what you want to accomplish with your horse. I do with my performance horses.
Each day, I have a plan – today I want to work on speed control, tomorrow I want to focus on stops, etc. At the start of each training session, I spend a good 10 to 15 minutes warming the horse up. It’s my chance to prepare the horse for the session, and it’s also a great opportunity to see where the horse is at mentally and physically for the day. Is he in a good mind frame? Does he feel off or sore?
Sometimes, even though I enter a training session with a set plan, depending on how my horse reacts in the warm-up, I change the plan to reflect what the horse needs that day. Just as much as you expect your horse to tune in to you, a good horseman tunes in to what his horse is telling him.