Opportunity Modified Date

Good morning all,

I am currently working on a report in the "Opportunity  Product Revenue History" and have been requested to provide a column indicating the last time the Opportunity has been modified-- at any level--whether it be a change to the" Estimated Close Date", an attachment added to the opportunity record or even an email recorded to the opportunity.

The limitation with the  "Modified Date" field is that it is only triggered by a change to any of the Opportunity header fields, not an edit at the "opportunity product revenue" table, "completed activities", etc.

Does any one have a suggestion of how to go about tracking the last time the overall opportunity has been changed, regardless of what table within the opportunity was modified?