Originally Posted by Mcspeed

Spading around the tree to cut the escaped roots. This is often done in advance to digging yamadori as well, it severs the big roots and tends to ramify the roots closer to the tree. You also don't have to leave the box inground for the roots to escape, pull it regular for different exposure to the sun. Afterall it is a good idea to rotate your trees for full exposure to the sun, the tend to grow towards the sun if left in one place.