%psql help

Hi all, I'm quiet new in this stuff, I have N psql users and N
databases, each user has a database and can connect  to it using his
psql account, however I don't want to allow that some user access to
another database that does not belong to him. I've modify my pg_hba.conf
file, and allow the access to the databases acording to his owner, but
once the user has connected to the DB it can change the connection to
another using this command : \c db1 user2, so my question is, can I
revoke commands?? or can I configure it per user?? or something??

Regards.