DiD S10: restore old (slightly modified) behavior for keeping Volk in-castle

data/campaigns/Descent_Into_Darkness/scenarios/10_Alone_at_Last.cfg

@@ -232,21 +232,6 @@
         [/unstore_unit]
 
         {CLEAR_VARIABLE stored_Darken}
-
-        # Make Volk hang out at his keep. We can't use a guardian since we don't
-        # want him venturing out to attack
-        [micro_ai]
-            side=2
-            action=add
-            ai_type=hang_out
-
-            [filter]
-                id=Darken Volk
-            [/filter]
-            [filter_location]
-                terrain=C*,*^V*
-            [/filter_location]
-        [/micro_ai]
     [/event]
 
     [event]
@@ -373,7 +358,38 @@
         {MODIFY_UNIT (id=Darken Volk) facing sw}
     [/event]
 
-    # In-scenario events
+    # This helps prevent Darken from getting himself killed easily by preventing
+    # him from leaving his castle
+    [event]
+        name=side 2 turn refresh
+        first_time_only=no
+
+        [modify_unit]
+            [filter]
+                id=Darken Volk
+            [/filter]
+
+            [movement_costs]
+                flat=99
+            [/movement_costs]
+        [/modify_unit]
+    [/event]
+
+    [event]
+        name=side 2 turn end
+        first_time_only=no
+
+        [modify_unit]
+            [filter]
+                id=Darken Volk
+            [/filter]
+
+            [movement_costs]
+                flat=1
+            [/movement_costs]
+        [/modify_unit]
+    [/event]
+
     [event]
         name=attack
         [filter]