"Not our man"
Translation:Nicht unser Mann
To be honest I'm not completely sure myself (I got this wrong too), but if I had to guess I would say that 'nicht' being at the end of the sentence has something to do with the negation referring to the verb of the sentence:
'Das ist unser Mann nicht' - 'That is not our man' (the verb 'is' is negated) vs. 'nicht unser Mann' - 'not our man' ('our' is negated)
Although it seems that 'nicht' could still go before 'unser' in the first example... Let me ask someone about that.
My girlfriend gave a vague confirmation of this, but this might be more helpful as it is much more comprehensive: http://german.about.com/od/grammar/a/The-Position-Of-Nicht.htm
TL;DR: "Nicht is an adverb, and so you will always find it either before or after a verb, adjective or fellow adverb. It usually precedes an adverb or an adjective, but likes to settle after conjugated verbs."
It also explains that nicht can go at the end of a declarative sentence, i.e. stating a fact. That's probably why we've seen this construction before; nearly everything we're translating so far are declarative sentences. (I think, unless I'm wrong and 'declarative' is some kind of linguistics jargon...)
Hope this helped!