I've saw much users asking for a mod to lock their own topic. Maybe it is a good idea if the users can lock their own topics after it's solved?
No, some users say "Lock please" after their issue is solved, but I rarely fulfill their wish. I don't like the idea of locking topics once solved, the topic should remain open so the user can continue to post about his/her problem, or other users can use the info about that particular problem.
But then the user can unlock it, right? If the user has enough info, then he/she can lock it. If he/she wants to add more info, he/she can unlock it.
To elaborate, a forum full of locked topics looks hostile, like if you post something it will immediately be closed, this is not the attitude we want to show new users.