For a Content DB backup (part of 2010 DB migration process), how do I set the SharePoint 2007 content DB to "read only" for the duration of the backup?
In a query window you would:
ALTER DATABASE <dbname> SET READ_ONLY;
And to revert:
ALTER DATABASE <dbname> SET READ_WRITE;
If you really want to do this with the GUI, right-click the database, select properties, move to the Options tab, and scroll down to the State section. There you can select Database Read-Only
and set that to True or False.