1. Trackers....

D. Can't work when the trail is too contaminated.

On the contrary, if a trail shows too much contamination, (alot of tracks are easily seen) then it will be easier for the tracking team to sort out the subjects tracks. Trackers will be looking for tracks leaving the trail (if the subject is on the trail they would have been found).

Track traps (muddy,sandy,etc) can be studied for tracks comming and going. the tracks that go up & don't come back are subject to further study.