How to setup an alert for no modifications?

How to setup an alert for no modifications?

I want to setup an alert that will send an email when no AD user account modifications where done the last 2 hours by a specific user account. Cant figure out how to do that, anyone with experience setting this up?
I tried using the "Modified Users" report profile and set the threshold of events to 0 the last 2 hours with a specific filter on Caller Username, but I receive an error that the threshold numer is invalid.