how do dba force developers to use schema name before table name

Welcome to the forums!
In SQL Server 2008 you could set up a policy to enforce this. In SQL Server 2005 there may be some third-party tools available analyzing this, but frankly, the best way to achieve this is to educate your devs. Tell them about the disadvantages of not using the fully qualified name and maybe threaten them to reject any change script without these fully qualified names. []