Here's an edited post I wrote previously about 'napping/barnsour/buddy sour'...
Why do horses 'nap', especially on their own? Primarily because they are nervous prey animals who don't feel safe away from their herd. They need a trusted and respected leader who must be considerate & respectFUL to earn that role. They can also learn from this nervous reaction that it's the best way to minimise unpleasant or uncomfortable work. Some horses are confident and assertive and overcome their fears and/or then attempt to take over the vacant or lacking(according to them) leadership role.
It is a relationship issue that you need to overcome by earning that leadership role so the horse can feel safe with you. I think what will help is working at home on desensitising her to a variety of stuff using approach & retreat, without overfacing her, and consistent and *fun*(for the horse too, not just you) training with the help of lots of positive reinforcement(reward) and as little as possible unpleasantness.
I would work on going out on the trail using approach & retreat tactics, both on the ground & in the saddle. I would *gradually* ask her to do more, go further, etc only after she becomes confident and willing with easier things - taking you to or thru the yard gate for eg. I would also be using positive reinforcement there too. A pocket of treats, planting treats in strategic places, leading her to grazing, a friend, giving her a good scratch *if she truely enjoys that*, etc...
As you can see in the above, I would do similar to appyfan, but I would try to ensure the retreat/return was *before* he got upset. Otherwise you're in danger of making this behaviour worse - he learns that if worried, he acts up & his friend will come back.
As you have said, you're also nervous of 'bad' behaviour due to previous experience. I think you need to get over this, as if you're nervous, he's not likely to have faith in your leadership or protection. He's had little training & presumably only with you, so this could become his major attitude about people generally. It could cause the whole situation to snowball and you will both lose further confidence in eachother. I'd work on your confidence on another good horse &/or get someone confident & considerate to work with your horse until he's solidly trained.
Regarding your 'side notes' here are some other bits I've written previously... Please disregard the bits that are inappropriate to your situation.
Without knowing what you've been doing besides kicking, how your relationship at the yard is, etc, I can only suggest some broad advice which you'll have to figure based on the hows & whys. I appologise if some of it may be stating the obvious or not appropriate for you're situation.
Most horses are pretty lazy when it's truly their choice. Without knowing how lazy or otherwise she is generally - not just ridden - I hesitate to take that lable on face value. It might be that she's learned to be like this because of all the kicking. It seems that she's had plenty of experience being desensitised to the pain of it, so is probably just enduring it without knowing how to alleviate it.
I would start on the ground and get her responding well there before I rode her. I would teach her to yield(respond softly without resistance or escaping) in all directions with *gradually increasing, steady pressure* rather than jabbing, as she has learned to endure. Start softly and gradually increase the pressure to a level of moderate discomfort(but not pain) and then just persist at that level, for as long as it takes until she responds. The *instant* she responds, in the smallest way - even a shift of weight - release all pressure and reinforce that behaviour. Repeat these exercises over & over until she is consistently yielding softly to your softest cues. Gradually ask for a little better - more steps, more speed, etc - only as she becomes confident with easier tasks.
In relation to things like her braciness & unresponsiveness under saddle, first and foremost make absolutely certain that there is no saddle pain or otherwise causing her physical difficulty. This is unfortunately a very common cause of negative behaviours. Also make sure you're riding in a balanced way, not on her forehand or on the reins. It will also pay to have her feet assessed for balance and her teeth checked if you haven't recently(the norm is about yearly for teeth floating). Would pay to have some lessons if you think your riding style could be contributing to the problems.
Once you're in the saddle, use the same steady pressure that you taught her on the ground. Don't automatically expect her to understand, but *teach* her. Sit up & squeeze with your legs, turning it into a gradually increasing squeeze with your heels. Persist until she yields. If(when) you need to back this cue up, I would begin tapping her rhythmically on the rump with gradually increasing pressure. If you think it will take more than you can manage with your hand, by all means, use a crop. Again, the instant you get the smallest response, reinforce it by dropping all pressure and rewarding her.
You need to remember this boy is a youngster with obviously little training. You need to *teach* him to yield to pressure, not just use pain & force to make him do things. Work towards your goals in small, easy steps. Make it clear & easy for him & reinforce whatever he gives you along the way, not punish him for not doing the whole exercise, or doing it imperfectly.