You should know your assets. If you know your assets, it's pretty trivial to write a script or program that checks when their certificate expires, sticks it in

You should know your assets. If you know your assets, it's pretty trivial to write a script or program that checks when their certificate expires, sticks it in a database, and alerts you when it's getting close to time to renew. Of course, if you don't know your assets, you hopefully at least know your IP space and can scan that.