If you want to feel challenged, try to teach what you think you know to someone who doesn't know it. :-)

Seriously when you try to teach someone you will find very quickly where the gaps are in your own understanding. You will need to go over what you think is true and revise it. And, as a bonus, you will have another person around who can serve as a "sanity check" and who you can work with on projects.

To find your victi^Wtarge^Wstudent I would suggest trying to discuss some of the more philosophical questions with fellow programmers. That is some of the why's and wherefore's. For instance what were the underlying issues that made a particular past incident more likely, and what could be done about it in the future? Find someone whose eyes don't glaze over, and you have a likely candidate.

Of course the same thing can be done online. But I think it works a lot better in person.