I have some ideas for the Citadel that I wrote down last night...
First of all, some Basic Assumptions...
* It doesn't need any SBG modifications that hinder climbing, since most enemies are assumed to by either flying or teleporting to reach to Stronghold.
* Alignment detection items / effects are of questionable value, since his enemies are equally likely to be good as opposed to evil.
* Traps / magic effects with low DC are virtually useless, since the biggest threat for his Stronghold is assumed to be small groups of relatively high-level opponents as opposed to great hordes of low-level opponents.
* It doesn't need any special protections against siege engines, as it isn't really a threat for a flying citadel.
Some Suggestions
* You could create sections of the Stronghold that have effects that target living creatures. Sahak has many minions which are Constructs, perhaps even some that are undead, which could control / patrol the area.
* You could, for example, create a special section of the basement that has a locked away Vampire, perhaps a previous intruder that Sahak captured. Intruders wouldn't know this and attempt to break into the given section, thus making them targets of the Vampire. (The good thing about it being a Vampire, is that a Vampire that is deprived of Blood will not be commandable, but it will attack anything thats living. Other intelligent undead wouldn't do that. I know a... cough cough... good Template if ya need one).
* Perhaps Sahak has assisted an Elven Lord when his forest was attacked by orcs or other elf-hating brutes. The Elven Lord in return gave Sahak some especially made Elven Ballistas that guards the stronghold against flying enemies. Even though Sahak is evil, he's intelligent and diplomatic, so its not unlikely he would assist an Elven Lord, as an opportunity to gain a valuable ally.
* The Stronghold would probably have intelligent trap combinations. Example of this. A long hallway with poisonous traps that all deal Con damage. Crossbow traps, poisonous gas etc. In the end of the Hallway, a Symbol of Death or Stunning (which both require Fort saves). I used this previously against my players, they hated me, which must mean its effective. After all, Sahak DOESNT play fair)
I made another critter that might be suitable for trap maintenance.
Trap Minion
Tiny Construct
AL: Neutral
HD: 1d10 (5 hp)
Init: +2 (Dex)
Speed: Fly 40 ft. (Good)
AC: 15 (+2 size, +2 Dex, +1 Natural Armor)
Attack: None
Damage: None
Face/Reach: 0 ft. by 0 ft. / 0 ft.
Special Qualities: Invisibility
Saves: Fort +2, Ref +2, Will +4
Abilities: Str 4, Dex 14, Con -, Int 14, Wis 10, Cha 10
Skills: Craft (Trapmaking) +10, Disable Device +8, Search +8
These minions are excellent for maintaining traps in their masters Stronghold. They fly around the Stronghold, avoiding suspicion by being invisible. Any traps that have been triggered are quickly repaired and reset by the small, spheroid minions.
The minions resemble small, floating spheres that have four tiny arms attached to them. This allows them to perform any Craft tasks at half speed.
Invisibility (Sl): At will, the minions can become Invisible as per the spell.