How to protect a db from an sa user fetching its schema

On a customer-owned SQL Server 2000, we've got our db placed, together with
other software vendors databases. How can we protect from that the customer
and\or the other companies from fetching the db schema of our db?

All parties are allowd to login with the sa account. Can we by any means
configure our db such that only we can access the schema, and the sa can
not?

Must all parties (companies) be given individual logins? Then, what about
the sa account? Using this, one is still entitled to the schema of all
databses, right?

Any web page were I can read about this?

Magnus


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