information_schema for all users

I wold like to make a plpgsql function that return column names and
their data types of a specific table.
I have done this using:

CREATE OR REPLACE FUNCTION _get_table_definition(refcursor) RETURNS
refcursor SECURITY DEFINER AS
$$
DECLARE
BEGIN   OPEN $1 FOR SELECT column_name as field_name, data_type as
field_type FROM information_schema.columns WHERE
table_name='_table_name';   RETURN $1;
END;
$$ LANGUAGE plpgsql;

but it works only with the database owner although i have used
"SECURITY DEFINER".
How can I make it works for everyone that calls the function?

I use PostgreSQL 8.1.4