theyre in the walls

code/game/objects/items/stacks/stack.dm

@@ -174,6 +174,7 @@ Also change the icon to reflect the amount of sheets, if possible.*/
 		if(R.on_floor && istype(usr.loc, /turf/open))
 			var/turf/open/OT = usr.loc
 			var/obj/structure/blocker/anti_cade/AC = locate(/obj/structure/blocker/anti_cade) in usr.loc // for M2C HMG, look at smartgun_mount.dm
+			var/obj/structure/tunnel/TUNNELBLOCK = locate(/obj/structure/tunnel) in usr.loc
 			if(!OT.allow_construction)
 				to_chat(usr, SPAN_WARNING("The [R.title] must be constructed on a proper surface!"))
 				return
@@ -182,6 +183,10 @@ Also change the icon to reflect the amount of sheets, if possible.*/
 				to_chat(usr, SPAN_WARNING("The [R.title] cannot be built here!"))  //might cause some friendly fire regarding other items like barbed wire, shouldn't be a problem?
 				return
 
+			if(TUNNELBLOCK)
+				to_chat(usr, SPAN_WARNING("The [R.title] cannot be constructed on a tunnel!"))
+				return
+
 		if((R.flags & RESULT_REQUIRES_SNOW) && !(istype(usr.loc, /turf/open/snow) || istype(usr.loc, /turf/open/auto_turf/snow)))
 			to_chat(usr, SPAN_WARNING("The [R.title] must be built on snow!"))
 			return

code/game/objects/structures/girders.dm

@@ -173,6 +173,14 @@
 			return do_reinforced_wall(W, user)
 		if(STATE_DISPLACED)
 			if(HAS_TRAIT(W, TRAIT_TOOL_CROWBAR))
+				var/turf/open/CONBLOCK = loc
+				var/obj/structure/tunnel/TUNNELBLOCK = locate(/obj/structure/tunnel) in loc
+				if(!(istype(CONBLOCK) && CONBLOCK.allow_construction))
+					to_chat(user, SPAN_WARNING("The girder must be secured on a proper surface!"))
+					return
+				if(TUNNELBLOCK)
+					to_chat(user, SPAN_WARNING("The girder cannot be secured on a tunnel!"))
+					return
 				playsound(loc, 'sound/items/Crowbar.ogg', 25, 1)
 				to_chat(user, SPAN_NOTICE("Now securing the girder..."))
 				if(!do_after(user, 40 * user.get_skill_duration_multiplier(SKILL_CONSTRUCTION), INTERRUPT_ALL|BEHAVIOR_IMMOBILE, BUSY_ICON_BUILD))