Any reason you couldn't have them access your website from an iPad? It'd obviously require either wifi at the rink or a 3G device, but if your original vision was for them to use the website then I don't see how that's changed.
Alternatively, I could really envision this being more of an app than a book, with interactive sections, animations of the drills, dynamic recommendations on what to run next, tracking of what drills have been done, roster management and ranking, etc. It sounds like you'd need to hire someone to write it for you, but iOS developers are everywhere these days as long as you have the money to pay them. Specialty apps like this can go for pretty good prices (look at GPS apps, for example -- some of those go for upwards of $100, and people pay for it), and you get all of the protections of Apple's app store (yes, people pirate iOS apps, but the vast majority buy rather than steal).
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