The net that trapped Rue

I've been wondering for a while: the spot where the net was placed, was it chosen randomly by the Careers? They had no way to know in advance the “trajectory” of the three fires set by Katniss and Rue, and they wouldn't have the time to place the trap for Rue between the second and the third fire as Rue was way ahead of them. So did they just positioned some traps through the forest and Katniss was just lucky to never get trapped during the period of time she spent wandering in the forest?