One other idea is if you truly want all new databases to have this user with this permission per K. Brian Kelley's example, you can create this user and permission...

The second command is explicitly disallowed:

exec sp_revokedbaccess 'dbo'

Msg 15150, Level 16, State 1, Procedure sp_revokedbaccess, Line 51

Cannot drop the user 'dbo'.

But once you've remapped the database owner to SA, the...