Q&A: Rescue horses, boring riders, why striking & kicking?

Episode 56: I answer listener questions and receive some feedback from Ron. 

I answered a question for Ron in a previous episode and he calls in to let me know that he has tried the methods and they are working well. 

Question 1: Hi, my name is Virginia. I'm calling from Westchester County, New York. Thank you so much for your podcast and learning so much. I recently rescued a gelding they think is between 15 and 18 years old. We think he has a new century. We don't know too much about his history, though. He came to the new barn underweight and I've been feeding a lot, but he's been very pushy on the ground and in the arena. He trots and canters off before I cue him. It goes to the gate and stops as if he's saying, I'm done. I want to just go back to my and eat, because when I do lead him to his stall, he pushes right through me. So any advice you can give would be greatly appreciated. Thank you so much.

Question 2: Hi, Stacy. Thank you so much for your wonderful podcast. My question for you is what prevents a well-trained horse from kicking out or striking out at its handler? I am kind of new to the horse running and have quite a fear of being around the hindquarters or the front end and within striking distance. And I'm looking for a good answer that's going to kind of give me peace. I for example, let's say I'm behind the horse, washing his tail, washing his lower legs or even on the side putting on his saddle. What prevents him from kicking out is there's one small thing that frustrates him. Let's say he doesn't like it when you wash his tail or he doesn't like it when you squeeze his lower leg when you're trying to get the water off.So what makes him say, you know what, I'm just going to handle this?  

So what prevents him from kicking me or striking out at me even as he respects me, even if I don't know even if what, but just what prevents him from striking out and kicking out if I do something he doesn't like? Is it just that there's a line of respect and he knows not to cross that?