date function

How do I change this function so that it shows dates like this 2003-05-03 and not 2003-5-3?
And I also want to add a parameter so that the user can choose if it should show :
2003-03-03 or 03-03-03

create function ShowDate(@indate datetime, @separator char(1))
returns nchar(20)
as
begin
return
convert(nvarchar(20), datepart(yyyy, @indate))
+ @separator
+ convert(nvarchar(20), datepart(mm, @indate))
+ @separator
+ convert(nvarchar(20), datepart(dd, @indate))
end

this will get your date the way you want it, except it uses . instead of - as a seperator. what programming language are you using to display this data?

select convert(varchar(20),date_field,102) as 'date' from table_name

I solved my problem by sitting up all night, but thanks for your input!