Relative sources with ArcGIS

One year with Arc and someone (professor) finally reveals a secret that I wish I had known in the past.

For a while, I thought Arc was tied to absolute sources. Move your file on your HD, lose your connection, and you've got to rebuild your map all over again.
Not so!
Under "FILE" in ArcMAP there is an option called "Document properties"
Click there and then click on data source options and switch the button to the second option, show relative path to the data source.
Phew.
Now you can reorganize without losing your maps!