It would be really excellent if links never got broken, but they do. Cite a page, and the next day the owner of the site hosting it moves it. Copying the contents is anathema to GoodProgrammers and those who care about respecting authorship. How can we prevent BrokenLinks?
You can't, but here is a simple idea to help not prevent, but to enable the rescuing of broken links. If, whenever a page is cited, the person citing it takes the time to find and quote an unusual phrase from it, then the original will most likely be findable by a search engine, even if it gets moved. It may even be findable by using the WaybackMachine.
If the phrase quoted is pertinent, this also has the beneficial side-effect of enabling a casual reader to decide if the page is likely to be interesting.
Basically, I'm tired of marking potentially interesting references with the tag BrokenLink ...
Please continue to do so, a recruitment is underway to to encourage a project to correct pages where BrokenLinks are found, making them Updated Pages. -- WikiGnome
[Note that this last annotation was made in 2011. The current year is 2014, and no such project has taken form. Broken links need to be quashed by hand, apparently.]
See: FixYourWiki, GoodWikiCitizenCategoryWikiMaintenance