security question

How good is postgresql security?
For example, If I have data that I do not anyone to see, including the programmer/dba, is it enough
to change the password to the only user?
If they have access to the raw files is there a way for them to somehow see the data?
can they copy the files to another postgresql instance where they have rights and view the data?

Basically, we have a requirement to put sensitive personnel information into the database, including
salary etc. and we don't want any employees, including the dba to have a possibility of accessing it.

Thanks
Sim