I have a huge bulky horse, Chester. I want to start jumping him, his hindquarters are amazingly strong. Sometimes his strides are off? He jumps to close and does this quick half-stride thing, and sometimes he jumps too far away and has to stretch out.... what is happening and how do I fix it?! Oh also, when I try to collect him or slow him down, he just flexes his neck insted of slowing down or collecting?!?!