Adds attach below option

config.def.h

@@ -35,6 +35,7 @@ static const Rule rules[] = {
 static const float mfact     = 0.55; /* factor of master area size [0.05..0.95] */
 static const int nmaster     = 1;    /* number of clients in master area */
 static const int resizehints = 1;    /* 1 means respect size hints in tiled resizals */
+static const int attachbelow = 1;    /* 1 means attach at the end */
 
 static const Layout layouts[] = {
 	/* symbol     arrange function */

dwm.c

@@ -147,6 +147,7 @@ static int applysizehints(Client *c, int *x, int *y, int *w, int *h, int interac
 static void arrange(Monitor *m);
 static void arrangemon(Monitor *m);
 static void attach(Client *c);
+static void attachBelow(Client *c);
 static void attachstack(Client *c);
 static void buttonpress(XEvent *e);
 static void checkotherwm(void);
@@ -405,6 +406,21 @@ attach(Client *c)
 	c->next = c->mon->clients;
 	c->mon->clients = c;
 }
+void
+attachBelow(Client *c)
+{
+	//If there is nothing on the monitor or the selected client is floating, attach as normal
+	if(c->mon->sel == NULL || c->mon->sel->isfloating) {
+		attach(c);
+		return;
+	}
+
+	//Set the new client's next property to the same as the currently selected clients next
+	c->next = c->mon->sel->next;
+	//Set the currently selected clients next property to the new client
+	c->mon->sel->next = c;
+
+}
 
 void
 attachstack(Client *c)
@@ -1062,6 +1078,9 @@ manage(Window w, XWindowAttributes *wa)
 		c->isfloating = c->oldstate = trans != None || c->isfixed;
 	if (c->isfloating)
 		XRaiseWindow(dpy, c->win);
+	if( attachbelow )
+		attachBelow(c);
+	else
 		attach(c);
 	attachstack(c);
 	XChangeProperty(dpy, root, netatom[NetClientList], XA_WINDOW, 32, PropModeAppend,
@@ -1417,6 +1436,9 @@ sendmon(Client *c, Monitor *m)
 	detachstack(c);
 	c->mon = m;
 	c->tags = m->tagset[m->seltags]; /* assign tags of target monitor */
+	if( attachbelow )
+		attachBelow(c);
+	else
 		attach(c);
 	attachstack(c);
 	focus(NULL);
@@ -1897,6 +1919,9 @@ updategeom(void)
 					m->clients = c->next;
 					detachstack(c);
 					c->mon = mons;
+					if( attachbelow )
+						attachBelow(c);
+					else
 						attach(c);
 					attachstack(c);
 				}