Best practice for multi-field unique key

[Tskutnik]

I have 4 fields in a table that when combined must be unique.
I know you can setup multiple fields as a combined key, but I don't really need these to be the key (I will auto number a unique key). I just need to make sure the same combination of codes is not entered twice.
Do I set this up as multiple key fields anyway?

 

[CJ_London]

Do I set this up as multiple key fields anyway? yes - does not need to be a primary key