Trying to ignore them.
Well, not completely. I will throw in an allusion or two to the fey (chiefly of the sort that it makes travel through forest easier) so that, although they make no appearance, readers are aware they exist. Ignorance on part of the characters is not suitable, they are battle-hardened heroes, and aware of such perils.
Allusions are the limit. (The stuff that I invented for this story, the backstory that inspired it, doesn't count.) Because it's a distraction. I need to focus on this story -- especially since it isn't even outlined yet.
Yes, I may paint myself into a corner, but a problem with the fourth book is better than no fourth book because no first book.
So, back to the outline!