arcgis desktop - Automatically calculating geometry area when adding polygon in ArcMap?

In ArcMap 10, I realize I can manually do this after the polygon feature is calculated by right-clicking the column in the attribute tables to calculate geometry or create a python script to do this but neither of these seem to allow me to automate this for new features without having to take those manual steps after the polygon is created and added to the table. I want this to happen automatically once the feature is created and shows up in the attribute table, much like the auto-generated shape_area column works. Maybe I can use those values to convert them to acres in a new column?