One of the classic rogue skills is the use of traps. I'm assuming you know what these are, but just in case: http://en.wikipedia.org/wiki/Caltraps
It would fit the whole ninja feel that the rogue has.
I'm suggesting this as a secondary attack for the rogue, in place of the alternating melee strikes. Once dropped, a caltrap would remain on the ground and just wait for an enemy to run over it. Could be useful for finishing off an opponent if he starts to flee.
What do you think?