I have a large pony that , while riding in the ditches, tries to put his head down to get grass every 5 steps or so. I pull him back up right away, but it is not enjoyable to fight him this often. I am not yet comfortable riding on the highway shoulder on the gravel area to avoid the grass area.... any advice? I've only been on him a couple of times. He is very well mannered otherwise and doesn't spook at things. I really do like him.