Continuing our look at broken external links to your website, we need to address the best way of monitoring them. As I mentioned yesterday, Google Webmaster Tools gives a good list of the problems, so the easiest thing to do is to make a regular appointment to check in there. A good website owner will create a list of things which should be checked monthly, weekly or even daily, so just add this task to your list as frequently as you feel is appropriate.
However, if you want an alert that will come to you as soon as there’s some untoward activity, use Google Analytics. Under “Intelligence”, there’s an option to “Create an alert”. Set this to fire off an email to you whenever the number of pageviews of your “404 error page” gets over a certain limit.
One final approach is to set the viewing of your 404 error page as a “Goal” in Google Analytics. This can show how visitors got to the page, and will highlight the traffic sources. It’s straightforward enough to set up reports which can be sent to you regularly showing this information.