Metal detectors will work, but not on the new stuff these people are putting in the logs. Ceramic spikes. I have hit old ceramic insulators in trees, and I would much rather hit a railroad spike.
I read an article a while back on ceramic spiking. In one case, the group that did it, then posted the area telling of thier deed, but another group then removed the signs. They claim they are not out to hurt anyone. I think the ceramic spikes prove that they could care less what happens tp the sawyer, mill workers, and thier families.