PL/SQL :: Create A Trigger To Check If Synonym Already Exists In DB

How can I create a trigger to check if synonym already exists in db and if exists then don't create synonym.

my work: ( this is just like an outline i prepared)

select * from all_synonyms;
declare
s_exists number;
begin
-- check whether the synonym exists
select 1 into s_exists from all_synonyms;
-- an error gets raise if it doesn't
exception when no_data_found then
-- DDL has to be done inside
execute immediate ' create or replace synonym';
end;
/