What a chunnel does that a bigger run cannot
A bigger run gives hens more of the same ground, and hens reduce any fixed ground to bare earth in time. A chunnel — a tunnel of arched welded mesh, low enough to step over and long enough to matter — gives them new ground every time you move it, without ever giving them the garden. Hens travelling a tunnel along the edge of a vegetable bed will work the path and the bed's margin all day, taking insects, small slugs and weed seedlings, while the mesh keeps their feet and beaks off the crop itself. The flock gets the ranging behavior it is wired for; the garden gets patrolled edges instead of excavated rows; and because the tunnel lifts and re-pegs in minutes, the route can follow the gardening calendar from bed to bed.
Sections that join tightly and lift easily
Build the tunnel from welded mesh panels bent into a low arch, tall enough for a hen to walk upright and stretch, in sections of a length one person can carry without wrestling. The joins are where chunnels succeed or fail. Overlap each section's end with the next and clip or tie them so the seam cannot spring open, and peg the skirts down along both sides so the ground line has no inviting liftable edge. A determined terrier or a mink needs only a hand's breadth of gap, and it will test the tunnel at its weakest point, which is always a join. Fit a closable door or a lift-out panel where the tunnel meets the run, and another at the far end if the route ever opens into a second area, so the flock's comings and goings stay yours to decide. A section of solid cover or shade cloth over one stretch gives the hens somewhere to pass through midday heat without abandoning the route.
Routing the flock around the garden
Think of the tunnel network as plumbing for hens: you are directing a flow of appetites to where they do good. Run sections along paths and bed edges during the growing season, across a finished bed once its crop is lifted so the flock can clear the leftovers and turn the surface, and out onto lawn edges where leatherjackets and other grubs draw them into useful work. Move the route before the ground under it goes bare and sour — a chunnel left sitting for weeks creates the same worn patch as a fixed run, just narrower. Keep tunnels off ground where the flock should not pick: freshly sprayed areas, and anywhere ornamental plants toxic to poultry grow within beak reach of the mesh.
Shade, ground wear and predator discipline
Long tunnel runs in full sun need their shaded stretch to be more than an afterthought, because a hen halfway down a tunnel has fewer choices than a hen in an open run. Peg a board or shade cloth over one section and make sure water is available at the run end the flock returns to. Inspect the ground line weekly as you would any fence, re-pegging corners the flock's own scratching has loosened, and shift sections a few inches sideways at each move so the worn line does not deepen into a trench. When the route changes with the season, the plan should be visible to everyone who works the garden: in KinsLe Family Sharing, the current tunnel route and the order of beds to patrol can live on the flock's shared profile, so a helper re-pegs the chunnel where it belongs rather than where it happens to fit.