I recently unlocked 'Foxiest of Hounds' and this is what I discovered:
- Cameras can become suspicious but NOT hostile (green is regular; yellow is suspicious; red is hostile)
- Robots can go hostile if they don't alert other guards or sound the alarm
- Tripping mines does not void the achievement so long as it doesn't alert other guards (be wary of frag mines)
- The crazy people on Panchea can go hostile because they are incapable of enabling the alarm (they just want to kill people
- Certain parts of the game where the enemies are supposed to be hostile (Saving Faridah, etc.) do not affect the achievement.
Funny thing is, I didn't even intend on getting 'Foxiest of Hounds'; I was working on my 'Doctorate' playthrough (reading all experience books) and was always taking the stealthy approach in preparation for the next playthrough on the hardest difficulty. After acquiring my last Ebook, I figured I might as well finish the game to get the Pacifist achievement and possibly 'Foxiest of Hounds' and I luckily got them both.