I’ve got old Comanche foot traps all over my ranch from where they camped. Basically a foot-sized three-foot hole with spikes. Most have filled in, but occasionally a cow or an oil field worker will find one (generally when laying guy lines before they lay a pad).
Pretty much a guaranteed lost foot, assuming prompt medical care. Much worse if you don’t have a crew around you with a van and a radio (and a safety kit with a tourniquet).
I suppose one could never tell how long they’ve been there.
Two parallel walls on the border. Put those in the no-go zone between the walls.