I've heard of " old schoolers" that use mortar patch for stopping bugs after pruning.. Nails can also come from hunters n tree stands along property lines... Makes for a bunch of stump chains..Just wait till you get some concrete poured down into a tree by an old school "arborist". That's a lot worse than the metal.
Kids with nails, making a tree-house are always fun. They nail boards to the tree, and 30 years later those nails are buried in the wood 15' up a tree. Dulls a chain every time.