I need some help. I recently started leasing a really nice horse but I've come across some issues I need help with. He is fine in the walk and trot, but I have some issues with him in the canter. He sometimes rushes away and when I ask him to slow down, he throws his head and continues to rush. When I do get him back to the trot, he rushes to canter again, and starts throwing his head when I ask him to slow down. He continues with that behaviour until the end of our ride. I think he may be anticipating me asking him to canter again, but I'm open for any suggestions and advice. Note: He isn't young. He has no soundess issues. His teeth are fine.