One of the most common forum issues is "I accidentally changed my site urls and now I can't login". In many ways, changing the site urls through the UI is too easy and too many non-technical users end up in trouble.
What about taking a leaf out of Firefox's book? Try to get into about:config and you get a warning that you have to click past. It should be possible to implement a similar popup if someone tries to change the site urls in Settings -> General. Given that genuine url changes are relatively rare, this would constitute a minor inconvenience to tech-types at worst but it could save a lot of panic and heartache elsewhere.