Metal in wood-hmm, and that being said, you have no major battlegrounds there. Where I grew up, 3-5´ beech trees@ 150´ tall are metal infested from bottom to most of the tops. Schrapnels, AP rounds, bullets of all kinds, bomb and mortar shell fragments... Those pesky Katuscha rockets are fine, they are usualy visible with their lenght. I´ve seen portions which were better to sell at scrapyard for "dirty metal" price than to have them at lumberyard.
But all in all, until the mill does not have x-ray it is still a kind of roulette. Smaller pieces under 1-1,5 ft of wood are quite hard to detect magneticaly, especially in wet wood.