Spotted a slow-motion sculpture while on a walk for errands:
The fence encloses a lot next to a long-disused fuel oil (?) storage / distribution facility. The county’s historic aerial photos suggest the trees have grown since the the building inside the fence vanished in the mid-1970s.
The Smell of Molten Projects in the Morning 
“Nature versus war: How helmets, grenades and guns discarded during World War II have been swallowed up by tree trunks in Russia”
https://www.dailymail.co.uk/news/article-2602084/Nature-war-How-helmets-grenades-guns-discarded-world-wars-enmeshed-tree-trunks-Russia.html
I’ve heard sawmills around here don’t accept trees from homeowners to avoid wrecking blades on embedded metal like wire, nails, and maybe fence posts. Sawing into an artillery shell would produce a whole different problem!
We’re on an old mill site/company town, and there are some interesting embeds. One guy cutting trees for us found a spike near ground level, and I’ve found one with my saw. I have one tree that’s immune from cutting, because somebody wrapped field fencing around it several decades ago. That fencing is nicely embedded all around.
I still have found boards nailed to trees at absurd heights in various places. One 2 x 12(!) has holes where the woodpeckers used them as a ladder. Evenly spaced holes up 10 feet.
Haven’t the saw mills heard of metal detectors.
AFAICT, metal detection would add enough cost to make the log not worth the effort, so it’s easier to just get “known good” wood from a commercial / new-growth (there being no “old-growth” wood around here) supply.
Not sure a metal detector would work on wet wood, anyway, unless it was going for magnetic anomalies. The eco-terrorists in California liked to spike trees because it did so much damage and was hard to detect.
Long ago, I had a short gig at Little Debbie, wherein I learned they do incoming and outgoing metal detection on all their lines. The best detectors came from the UK, because they had deep experience with food from fields covered with wartime debris. I expected similar expertise in Germany, but the Brits evidently got there first and ruled the biz.
Took me by surprise …
Shameless product promotion…
http://www.metaldet.fi/eng/tuotteet/tuotteet.html