What little fiction I have that is remotely 'erotic' are in ebook format on my phone.

You could get pretty creative with that, however it might also draw more attention to them. If you're going to do it, I'd say do that to more books than just the ones you're trying to hide in sight. The only other thing is that some people might assume they're journals - which leads to the issue of whether or not you can trust the people in your household to respect that boundary.

If you have a lot of books, maybe you could pick a less conspicuous shelf and stack a few towers of books horizontally. You could place the books you don't want to call attention to on the bottom and strategically turn the spines backwards for those and some others throughout the stack. If you have ocd about things like that, this will probably drive you crazy but if not you can morph this idea into something you find visually stimulating. When you have stacks like this people are less likely to go to the extra effort to uncover the books on the bottom. You could even do the covering thing with all the books in the stack.

When I was reading your post I had a mental image of a shelf of books with homemade book covers made from an assortment of colorful scrapbooking paper with varied designs. Which would probably be a pinterest craft project my best friend would be all over.

Excellent ideas everyone! I am thinking of incorporating these in some way, to be aesthetically pleasing and save space. I will probably color/fabric code the covers and do this to all my books. I will mount them in some clever way, with my "preferred" far out of reach and labeled something undesirable.