Ears are a separate criteria from all the rest. I love one phrase that Pat Parelli uses, "Isolate, Separate, and Re-combine." Each criteria is trained as a separate behavior then combined for your finished product. When I teach it, I also use it as a "default behavior." In other words, in the absence of any other cue, look at me and prick your ears and you very well may earn a treat! As a clicker trainer, my pockets are very rarely empty. Now mind you, if I am getting that behavior in combination with being on top of me, that is not going to earn the treat. But if they lift their necks and give me that special warm look with pretty ears, Click and Treat.
Another thing to consider in future training is what is known as "first order of learning." In other words, whatever they learn first is retained the best. It is one of the behaviors they will try if they are begging. My horses are not all over me even when I have food, but they very well may try a few behaviors out to see if the slot machine might be paying out today. LOL
When you are working specifically on ears, you probably will want to be on the other side of a stall wall or something to keep them out of your space. Then just stand back and wait. As soon as you see the ears go up, click and treat. Continue doing this for 5 minutes or 20 treats. Then say "all done!" and let them know what a good boy/girl they are. If you can do several sessions in a day, that would be great. When they are offering the behavior on their own, you can add in a cue. Just before you know they are going to give it to you anyway, do whatever you want to cue them with and when they give the behavior, C/T as usual. Since I want this to be a default behavior, I want them to give it to me whenever but I also definitely want it on cue. If you do NOT want a behavior as a default, once you start getting the behavior reliably on cue, you will stop clicking and treating when it is off-cue. Now mind you this is VERY HARD! Some of your very best approximations of the desired behavior will happen once you withhold the click. That is also a way to strengthen behavior, but that is an advanced concept. One other thing to consider is behavior duration. There are a lot of sites on the web about clicker training, if you choose to go that route. Regardless of what method of training you decide to use, I can't recommend highly enough that you read the book, "Don't Shoot the Dog," by Karen Pryor. It is the bible of positive reinforcement trainers.
Good luck, and have fun with your horses! As far as I'm concerned, training my own animals is what is "fun" about them. I love the communication, the rapport, and the joy that comes from achieving a goal together. I do work with a coach, but the actual training is done by me from my own farm. I have had my horses in training before and enjoyed it immensely also, but to me there was still something missing in that scenario. When I won my first Grand with my own horse that I trained myself, I thought I had been transported to heaven.
Hope you get there too, someday soon.