Dungeons in Decline, seige conditions and desertion

Watching historic siege videos on star forts

Once monsters at dungeon defcon 3 or 4 things are desperate

They put in extra traps, lock and barricade doors and if possible erect barricades.
Civilians if possible will be sent away to kin or allies.
Wandering monsters are scouts and withdraw to gather a larger counterstrike force 

Here is some tables for when a dungeon is this bad
Add an extra one every visit

d12 New Dungeon Defence
1 Rolled a boulder or caused a collapse of select tunnels
2 Barricades manned by archers been set up, if attacks getting through or climbed they might withdraw and set the barricade on fire. Also good choke points for monster magic
3 A new more bloody war leader or holy person take over, dungeon adopts more bloody religion and fighting code
4 Vermin everywhere and food scarce d6 1=rats everywhere now best food source 2=fleas! everyone -1HP if infested 3=parasitic thread worms cause bloat and infectious, host becomes afraid of spicy food or anything worms dont want you to do to your body 4=huge stinging flies 5=giant rats 6=huge ants
5 Monsters all sick, -1 morale, HP, mov. Diareah everywhere, stinks like a sewer, monsters not using latrines as to dangerous to reach
6 Starvation with evidence of monsters eating each other (see how evil they are!), +1 morale if they see enemies who might be edible and might even stop in a fight to eat if fail a morale test near a tasty corpse. Some might have visions of evil spirits from these vile acts and their religion may be corrupted more even becoming lycanthropes or other monsters
7 Locked dangerous creatures in rooms as a surprise
8 Monsters kidnap hostages they can torment, threaten or strap on their defensive barriers
9 Allies or rivals invited in, even rival traditional enemies are better than falling to humans
10 Strengthen all entrance gates and double all guards
11 Lure adventurers with wounded carrying a sack of mostly copper coins into an ambush. Any ruse to lure the enemy into a gauntlet or kill zone 
12 Hire a spellcaster of any type available. Curse treasure and make magic traps or monsers

d12 Desperate Tactics
1 Pretend to have plague with makeup and some corpses, pretend to caught and have sores. Or will throw diseased corpse in the water supply of adventurers
2 Pretend to have become berserks, will scream, gnash teeth, bite sheilds and eat funny mushrooms to foam at the mouth. Maybe it works
3 Hurl wasp nests or bee hives
4 Suicide squad +2 morale leads counterattack while rest support with missiles
5 Incendiary squad with burning oil and torches, possibly spells
6 Monsters all using poisoned (+d4 after 10 min if fail save) or infected weapons (save vs disease)
7 Dead are raised as undead thanks to an evil priest here to help the dungeon
8 Accept the offer of an evil wizard and minions for aid  
9 Faction of the dungeon tries to negotiate surrender or withdrawal, possibly becoming allied or defectors with a good deal 
10 Get allies to attack local human camps and settlements on behalf of the doomed tribe
11 Make a deal with a monster like a demon or a dragon
12 Everyone takes poison and/or charges nearest enemies

d12 New Dungeon Dressings
1 Dead inhabitants made a suicide pact rather than face adventurers
2 Freshly gnawed bones of local inhabitants turned to cannibalism
3 Graffiti that abuses and curses invaders
4 Graffiti showing faction power balance changes 
5 Graffiti reveals the rise of a new cult influence on monsters in desperation
6  Broken weapons and signs of another group or faction taking advantage of decline
7 Faeces everywhere and flies from monster diarrhoea
8 Everything of value stripped and carried away in a hurry
9 Signs of rituals and religious paraphernalia, offerings before shrines 
10 Art made from human corpses to scare away humans

11 Signs monsters deserting their stations or understaffed

12 Angry poltergeists and petty hauntings of angry war dead