If we abandon the back door idea Alistar will pull the boards off. Taking 20 he gets a 25.
Keezheekoni speaks up before Alistar starts ripping into the building. "If we can't find any obvious signs of entry, perhaps we should sit in wait for these slavers to show up. If they truly are using this place for nefarious purposes, then any damage done may alert them to our presence."
"If they are using it and we can't find an entrance it seems unlikely we will see people coming and going as the slavers are likely using a secret entrance. I will wait if that is what people want to do."
Perception: 1d20 + 14 ⇒ (2) + 14 = 16
Though his keen eyes and ears didn't alert him of any hidden entrances, Tiarsus knew sometimes the physical realm was not the only one which held tells to passages.
"I'll concentrate on seeing if any sorcery is about the place. Other than that, I think Keezheekoni is right: Damage will alert them."
He shook his head in frustration. "Nothing I can sense. I think waiting is the best bet - at least we'll see how they exit or enter."
That's a good idea you should be able to detect through the wall and cover the whole area of the shack.