Cut into a limb of a tree and engrave your 12-word seed in the interior wood, then reseal the opening so the tree can heal over with bark again and look normal.
Mark the tree limb in a way that's inconspicuous, yet reliable to find again.
Discussion
How would you retrieve it later? It'll just heal over and be eraced. And however you cut it off again to try and find the seed it'll never be exact. No way you'll be able to retrieve the seed again.
You'd have to put the tree limb through an x ray or a cat scan or something to find the scarring left by carving the seed 🪵