There is a fairly easy solution to the horse cutting corners...Simple Steps
cutting corners. It begins, as solving all problems begin, at the walk. The walk is the slowest pace and the easiest pace to control in a horse, and it is where
all training begins. Practice riding your horse at the walk around the
arena, making him walk into the corners to a point where he almost has no room before allowing him to turn; at the same time, apply the leg that is facing the center of the arena (inside leg) behind the girth
firmly. This tells the horse that he is not allowed to cut corners. Do
this at each corner of the arena that you come to, each time applying
the inside leg firmly; thus telling the horse that he has no choice but
to come into the corner. You will want to do this in both directions, which will teach the horse that he must always stay to the edge of the arena when riding a corner; also, praise him each time he comes through
the corner without fighting your aids, this will really enforce his good
behavior and his desire to please you.
Once you have him going nicely through the corners at a walk using those signals, and you feel confident that he is doing well, try it at a trot. That way you can tell
if he is ready to listen at the faster pace. If the horse continues to
listen to the aids, reward him with praise and make your signals to him
softer. If he chooses to ignore your aids, bring him back to a walk and
resume doing the exercise at a walk, cuing him strongly with your inside
leg behind the girth and walking him almost into the corner. This tells
him that to not have the aids applied sharply, he must come into the
corner. Once he is obeying you again, try it at the trot again. Each
time he does not listen at a faster pace and starts to cut corners
again, bring him back to the walk and use your signals strongly.
As he becomes more compliant and listens at the trot, you may lighten your
aids-use your legs softer and give him more rein to allow him to pass
through the corner without cutting it. It will tell him that his good
behavior got you to trust him and he will be happy to please you. Trust
him, but if he goes back to the old behavior of cutting corners, rectify
the problem immediately by making him go back to the walk and pushing
him into the corners. Eventually he will learn that to move at the
faster pace he has to come into the corners smoothly and avoid jerking
in toward the center of the arena.
