The problem is that there are only so many concepts one can cover. The course structure, as @justinpombrio notes in another comment above, is that after an assignment comes due, the next class discusses the solutions. Essentially, once I publish all this, I effectively can't use these materials again in a course.

Yes, I know about the problems w/ security through obscurity, etc.

So for now, it's only an in-person course at Brown (and a few other universities that have been picking up this approach).

Sorry, I know, it sucks. But I don't know of a better solution that satisfies all constraints.