Borrow checker puzzles

Hey, I'm looking for a way to get a better understanding of the borrowing rules.

I had this idea that I think someone probably has came up previously, but I'm not able to find.

I'm looking for some kind of couse/book/tutorial with borrow checking problems.

For instance, It could present a piece of code that won't compile until you annotate it with explicit lifetimes.

It would not be real architecture problems. Just puzzles to help you understand corner cases of borrow checking.