The right thing to do here is to put the book or course into "Stealth Mode". That way the book or course will not show up on Leanpub any more, but you can still work on it.
Please note that if your book or course is currently published, before you can put it into Stealth Mode, first you have to unpublish the book or course.
To put a book into Stealth Mode, please go here:
...making sure to replace YOUR_BOOK with your book's unique web address.
To put a course into Stealth Mode, please go here:
...making sure to replace YOUR_COURSE with your course's unique web address.