Help me design a tactics computer program

Just downloaded Guess the Move yesterday and I think it is magnificent, really useful indeed. Anyway, in terms of a tactics trainer I think what is definitely missing is defensive tactics/awareness trainer, based along the lines of Heisman's book Looking for Trouble - Trouble Trainer?

I know that standard tactics trainer does have some defensive puzzles in there but not many and I think that it is a major blind spot in many people's play, certainly below a certain level 1600/1700 and certainly in mine. I don't know of any such program around anyway, even books are heavily weighted in winning tactics and mates in .../'white to play and win' with hardly anything around to help you reinforce your sense of danger in looking for you opponents threats and acting upon them, either defensively or with aggressive counter play.

Anyway, this was just a thought and I think such a thing would be very useful, though in my opinion nothing will beat GTM as this is just the best chess software I have come across. Thanks.