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"