Let us all know where you purchased your book or video from; some sources are hard to find. For example, for mules and donkeys, I really like the classic training (based on basic dressage principles) espoused by Meredith Hodges in her book "Training Mules and Donkeys" and the DVDs/videos that go with the book. Her books are hard to find unless ordered through her business, luckythreeranch.com
I have other books I like but I (including some REALLY old dressage books) but I am always trying to learn more, to find the explanation that works for me of something I have been struggling with.