What are some cute horse costume ideas for Halloween?

Halloween is coming soon so I've got to get ready for our costume party at my rodeo. I've never dressed my horse up before so im not so sure what to do. I don't really want to spend much money. He's tall, thin, and sorrel (copper-red). I'm gonna have to run on him so costumes that can't fall off are a good idea but I'm up for anything. Thanks for your help! =D