I've been working with my gelding on being more soft and to come back to me when asked. He is appendix and naturally carries his head high. He knows to give to pressure, sometimes he just refuses. This is something we will probably always have to work on during the week. My question is, during a run, he can tend to get up hill/high headed. I feel too high for him to use his body correctly and it's totally disengaging his hind end. I don't want to take his head away from him completely and I don't expect him to get as low as a cow horse but we definitely need some help in this area. I was considering trying a tie down or bonnet when running just to give him that little reminder when he hits it. I'm looking for any other suggestions as well. We work in a very very light bit during the week to keep him soft and work constantly on breaking at the pole, I'm just looking for something that might give that little extra help we need during a run. Thanks!!! 

The first things that come to my mind are saddle fit and long toes.  I believe that most hight headed horses start from lack of core that could be caused in part by long toes.  The horse has to compensate for the extra time before the foot breaks over by hollowing out their back.  It doesn't matter if you are shoeing them every 6 weeks if you have excess toe.  

The second thing is getting them to lift their back.  Stretching on the ground is a great start.  Fingers under the belly behind the cinch area and add pressure until the back lifts.  The more you do this the less pressur you'll need.  When the back comes up the head normally starts to lower and the butt engages better to help them drive from behind.  Since your horse doesn't do this naturally you'll have to start over a bit and as you ask for things at the walk and trot I'd advise to move your spur a little further back and sit more on your back pockets.  I've gone as far as sliding my saddle back a few inches for slow work to make sure I'm not riding the front end.  He isn't use to using himself this way so it's going to take time to get it consistent.  

Good luck!