I've been leasing a mare for about a month, and want to do gaming. I ride her in a plain O-ring snaffle. I've been doing quite a bit of work on stopping, and I almost always back her up after stopping to really engrave the whole concept of stopping on her hindquarters, which I have done with previous horses and it really improves their stops. I do lots of rollbacks as well, but her stop hasn't improved much at all. When I ask her to stop, she resists the bit a little, and slows down, but takes forever to come down to a complete stop. I've seen her stop really fast, and had her do it with me on her a few times, so I know she is completely capable. What am I doing incorrectly, and how can I improve her stop?