Hi and welcome!
There are already many threads about the exercises and drills you can do with your barrel horse. I'm sure you can look around and find a few exercises you can do with your horse..There are also many drills you can do at the different levels of experience.. barrel tips Keep him from getting bored? What drills do you do? Barrel Racing Training tips please (:
When he is starting to expect your turns and won't set up for his pocket correctly go past the barrel..Just keep trotting right by it, don't let him turn it. After you've went past the barrel turn the opposite way and continue to the next barrel, go past it too and turn away from it..Do this a few times throughout the whole pattern and he will get used to having to listen to you instead of following repetition. After you've done this a few times I would go back through the pattern at a walk or trot and make wide turns around the barrel while keeping him rounded and collected..When doing these different drills and exercises you constantly want to keep him on his toes, always do something different and not the same thing over and over again, that's what causes him to expect the turns and other things..When doing your turning drills I would also bring other objects into play, not just barrels..Find a few odd things around your arena like cones, tires, buckets, and other weird things to change it up. You can set up different patterns with like 5 barrels and never do the same pattern..There are countless different drills and obstacles you can put him through..You don't always have to do barrel drills or exercises either..Take him on a trail ride or do some other discipline to constantly keep his mind working and not making every ride about "work"..Just get creative with it and remember to have fun.