Stop a query if cross database queries are requested in the command?

Hi,

is there a way to raise an error if a user run a SELECT statement which contains specific keywords?

here my scenario:

I want to insure that if a user open a connection to a specific database and try to execute a select statement which  access another specific database, then raise an error.

example:

connection to the DB1 database, query= Select * from DB2.dbo.Table, then raise an error

connection to the DB1 database, query= Select * from DB3.dbo.Table, then NO error (this DB3 access from DB1 is permitted)

The user has access to the DB1 and the DB2 databases, I want to insure that 2 databases are never used in cross database queries.

is it possible to filter this in SQL Server? (using database triggers, server triggers or session event?)

thanks.