As a small kid I was enthralled when I saw a western and the indians hid to ambush the wagon train in "Spider Holes", little one-person holes dug beside the trail, totally camoflauged by putting dry dirt on a blanket covering the hole.
Of course things can go wrong with such a hole if it rains a lot, if someone steps in the hole, if some small critters move into the hole.
Rain can be planned for by sloping the earth slightly away from all edges of the hole and digging a deeper spot at the bottom of the hole for the rain to go, having some small boards or gravel to stand on.
Operating a scare from a hole in the ground, in the dark , is not something that everyone, as employees will feel comfortable doing.