Here is an excerpt that may be helpful from my Dad's 1950 Trappers Bible booklet on constructing a hole set.
THE “OLD INDIAN” DIRT HOLE SET
The “Old Indian” set is an improvement over the commonly made dirt hole set. First, dig or chop out a trap bed the correct size for the trap being used. Make it deep enough that when the stake is driven or the grapple hook is placed in the hole and covered with one inch of soil, the trap will set one inch below the surroundings. Place the covering over the pan. Bed the trap solidly so it will not tip if the animal steps on the springs or jaws first. Always position the trap so the animal walks into it between, not over the jaws. The trap pan must be level. Selecting the finest soil, cover the trap with ¾ inch. Starting at the back edge of the trap bed and off center one to two inches to the left, dig a tunnel gradually deeper until it becomes a hole. The hole should be placed back of the trap pan six to eight inches for fox, and nine to eleven inches for coyote. The hole should be about four inches in diameter and at least eight inches deep, slanting back at a 45 degree angle so the animal must approach from the trap side to look into the hole. When the trap is covered the right depth, use more soil to build two ridges about two inches high. Start at the mouth of the hole and come back one foot just clearing each jaw with the ridges. Make another little soil pile just at the mouth of the hole so the animal must come in closer to peek into the hole. When completed the trap sets between the ridges, and just back of the little pile at the mouth of the hole. The two ridges and little pile of soil at the mouth act as guides. The trap is in the lowest place between the ridges and off center one or two inches to the right of the hole. Additional small weather-stained, natural looking branches may be used as guides on each side of the jaws. They must be firmly planted and pointing out from the jaws at a 45 degree angle. Place lure and urine as previously described. Place any excess soil, roots, stones, etc. on your kneeling pad to be carried from sight. Carefully examine the area and cover any signs of your having been there. All must look natural. Learn to make sets as quickly as possible to avoid leaving excess human odor.
Ace
