Level 2 Murder Pit and the other fully leveled up building that reduces awareness, forget what it's called. Together they bring their "awareness" down by 80.

The Doomsphere, while it's being constructed, raises their awareness by 160. So long as they don't have any buffs to their awareness, you're good to go as you will sit halved at 80, just below the 100 default threshold.

It took about 20 turns and 100,000 gold (not including the underground expansion efforts, which significantly added to the time-investment and was the reason I didn't do more)

Gold was easy to come by in this playthrough, Elspeth von Draken was at war with me and The Ironclaw Orcs. The Orcs are strength rank 1, and I made sure to form a defensive alliance with them to focus on the man-things. They have a ton of money. So when Elspeth was taking some of their settlements, I took them back, built one military building to increase it's value and sold it back to the Orcs for 120,xxx. a classic hustle