I’ve heard of hugokultur. Unfortunately, neither I nor my husband can dig trenches, and he probably would balk at renting a backhoe. (Wish I could afford to buy him one -— he’d be digging up the whole neighborhood)! And Lord knows we’ve got plenty of tree limbs and wood scraps we could bury!
I think you can also build them by laying the stuff right on the ground and then covering it with mulch, grass clippings, dirt, compost, whatever.