A new Googler and a Google Analytics Expert, Daniel Waisberg, some days ago posted on Google+ profile of Google Analytics, a Tip for setting up custom alerts just in case you receive a higher 404 page requests.
Now as all of you know, there is nothing as bad as landing on a 404,page not found, error page for a user. Just in case you have a page who starts showing 404, page not found and is even listed in the Google rankings then surely it is going to cause a very bad Bug which makes monitoring for this error essentially important.
Now most of the people monitor their error Logs or check a specific page through Google Analytics. But surely it shall be of great importance if you have Google analytics covering your back by alerting you whenever such an error occurs on your website.
Now Daneil explains the process in following way on Google+
1. Login to Google Analytics
2. Click on “Admin” on the top-left navigation (orange bar)
3. Click on the profile you want to create the alert
4. Create a Goal using the 404 URL
5. Click on “Custom Alerts” and create a new alert
6. See image attached
See the image below for a greater understanding