ZOMDir is a human edited directory. Everyone is able to edit almost everything. Texts, subjects, locations and of course links. As a consequence everyone is also able to remove a link. This is very powerful in the flight against linkrot.
Due that linkrot is a huge problem there is an automatic link removal tool. Once in a while links are tested. When the linked webpage doesn't response normally, the link will be removed directly.
Such a tool seems to be necessary. For example DMOZ.org has pmoz.info and Robozilla to fight linkrot.
Recently I learned that Wikipedia use bots to fight vandalism. For ZOMDir that isn't necessary yet, however I will add an anti vandalism bot on the product backlog with for the moment a very low priority.