William didn't know that the main reason behind the delay in his guild masters' arrival was thanks to his bad reputation as a trouble magnet. The girls were convinced he wanted those masters to fight a new enemy or stop a disaster or something.
If he heard them saying this, he'd laugh to his heart content. And yet he didn't even notice the delay at all. He was totally absorbed in laying down the formations, thinking if two layers were good enough or he'd need to lay down more.
The fortification he made in the underground city was to contain the explosion, but the fortifications he planned to do here were to protect this area from the aftermath of the explosion.
He didn't believe the formations he laid at the city would be enough to stop the explosion. That was why he considered adding more layers of defence here.
