Caltrops: a nonmagic stackable tool that when applied creates a “caltrop trap” on your space, which damages / immobilizes / slows the first monster to enter it. Rangers and rogues excel at using them and possibly get some bonuses from them. Not difficult to untrap, though it would be nice if some caltrops could gradually be lost in the process. Maybe spreading caltrops consumes five or so of them, and you won’t always get five back during an untrap.