How to avoid users from viewing functions code

Hi
the problem is to avoid users from viewing functions code (in general db
structures) when connecting to db by means of pgpadmin client.
My db contains several tables and functions and I need to make users viewing
only a restricted
number of tables. It works for tables, as it's possible to define access
policies,
but I didn't find something like that for functions.
The result is that everyone can see functions code from all pgadmin (II & III)
clients using basic user account.

This is my PostgreSQL Client Authentication Configuration File

local all all trust
host all all 127.0.0.1 255.255.255.255 trust
host all all 10.43.13.75 255.255.255.255 trust
host template1 basic 0.0.0.0 0.0.0.0 md5
host servizio basic 0.0.0.0 0.0.0.0 md5

Is there any idea?

Thanks Paolo Mattioli