Hello! I am new to the Uni but not to horses. I adopted 2 mustang geldings last year. One of them is coming along famously. The other...meh. I recently brought in a new mare who is here for training and now my mustang has decided that his new fun trick is to bolt while he is being led. I tried using a longer line in order to give him to run room but to no avail. He hits the end of the line and broncs it out until I have no choice but to let go. Then back to the herd he goes. I need help.