Salesforce Junction Objects

Question

I'm looking for some help from all of you salesforce professionals. My contacts are stored in a custom object called programmes. To master detail linkages between contacts and programmes, I designed a junction object. I don't want to associate the same contact with the same programme. I attempted triggers, but I couldn't figure out how to test them outside of the sandbox.

I went back to the basics and created a Unique text field. I tried to use default value but EVERYTHING i write in that crap is wrong -_-. I tried Contact__r.Email & "-" & Program__r.Name but to no avail.

I tried workflow rules with a field update but my field update NEVER runs.(Yes I did activate the workflow rule) and I didn't know what to write in my rule's code.