Caddy as anchor.
How a 4-inch cardboard box becomes the dead weight that catches every flying tee.
The mechanics
A full caddy with 4 tees, 4 cords, and the foam insert weighs about 60 grams. That is not much. But you do not need much weight to catch a tee returning at gravity speed across 28 inches of cord.
Why it does not get yanked out of position
The cord is fixed length, not elastic. When the tee reaches the end of the cord's travel, the deceleration is gradual (the cord catches, the tee swings back). No yank, no jolt to the caddy.
Where to place the caddy
Just outside your stance, on the side of your trailing foot (right side for righties, left for lefties). The cord runs parallel to your stance line, not across it. Out of the swing arc.