A few qdel fixes.

code/game/objects/effects/effect_system/effect_system.dm

@@ -38,7 +38,7 @@ would spawn and follow the beaker, even if it is carried or thrown.
 /datum/effect/effect/system/Destroy()
 	holder = null
 	location = null
-	..()
+	return ..()
 
 /datum/effect/effect/system/proc/set_up(n = 3, c = 0, turf/loc)
 	if(n > 10)

code/game/objects/effects/landmarks.dm

@@ -6,7 +6,6 @@
 	unacidable = 1
 
 /obj/effect/landmark/New()
-
 	..()
 	tag = text("landmark*[]", name)
 	invisibility = 101
@@ -63,12 +62,11 @@
 			xeno_spawn += loc
 			qdel(src)
 			return
-
 	return 1
 
 /obj/effect/landmark/Destroy()
 	landmarks_list -= src
-	..()
+	return ..()
 
 /obj/effect/landmark/start
 	name = "start"
@@ -81,11 +79,11 @@
 	tag = "start*[name]"
 	invisibility = 101
 	start_landmarks_list += src
-
 	return 1
+
 /obj/effect/landmark/start/Destroy()
-	..()
 	start_landmarks_list -= src
+	return ..()
 
 //Costume spawner landmarks
 
@@ -242,7 +240,11 @@
 
 /obj/effect/landmark/start/depsec/New()
 	..()
-	department_security_spawns |= src
+	department_security_spawns += src
+
+/obj/effect/landmark/start/depsec/Destroy()
+	department_security_spawns -= src
+	return ..()
 
 /obj/effect/landmark/start/depsec/supply
 	name = "supply_sec"

code/game/objects/structures/girders.dm

@@ -231,20 +231,16 @@
 	switch(severity)
 		if(1.0)
 			qdel(src)
-			return
 		if(2.0)
 			if (prob(70))
 				var/remains = pick(/obj/item/stack/rods,/obj/item/stack/sheet/metal)
 				new remains(loc)
 				qdel(src)
-			return
 		if(3.0)
 			if (prob(15))
 				var/remains = pick(/obj/item/stack/rods,/obj/item/stack/sheet/metal)
 				new remains(loc)
 				qdel(src)
-			return
-	return
 
 /obj/structure/girder/displaced
 	name = "displaced girder"
@@ -264,20 +260,16 @@
 	switch(severity)
 		if(1.0)
 			qdel(src)
-			return
 		if(2.0)
 			if (prob(30))
 				var/remains = pick(/obj/item/stack/rods,/obj/item/stack/sheet/metal)
 				new remains(loc)
 				qdel(src)
-			return
 		if(3.0)
 			if (prob(5))
 				var/remains = pick(/obj/item/stack/rods,/obj/item/stack/sheet/metal)
 				new remains(loc)
 				qdel(src)
-			return
-	return
 
 
 //////////////////////////////////////////// cult girder //////////////////////////////////////////////
@@ -330,16 +322,11 @@
 	switch(severity)
 		if(1.0)
 			qdel(src)
-			return
 		if(2.0)
-			if (prob(30))
+			if(prob(30))
 				new /obj/effect/decal/remains/human(loc)
 				qdel(src)
-			return
 		if(3.0)
-			if (prob(5))
+			if(prob(5))
 				new /obj/effect/decal/remains/human(loc)
 				qdel(src)
-			return
-		else
-	return

code/game/objects/structures/lattice.dm

@@ -31,7 +31,7 @@
 		if(locate(/obj/structure/lattice, get_step(src, dir)))
 			L = locate(/obj/structure/lattice, get_step(src, dir))
 			L.updateOverlays(src.loc)
-	..()
+	return ..()
 
 /obj/structure/lattice/blob_act()
 	qdel(src)