How to deny remote backups ?

Hello,

First of all sorry about my bad command in english.

I have an Internet server with postgres 7.4.7, planned to give remote db
services.
I have several offices, with client programs that connect to the internet
DB server vía a SSH tunnel.

The user DB that connects to the remote DB has insert and delete permissions
(he is the owner of the DB).

The question is ... how can I block or forbide the remote DB duplication
?. I think that a remote person that knows the user DB and his password,
can connect to the DB and make a pg_dump of the DB.

Is there a method (with SQL user permitions, templates, newest version of
postgres, ...) that forbides the remote dump of database or its structure
?
I want , for example, only the postgres user can make a local backup inside
the server.

Thanks.