Great Black Mountain was quite near to his own territory. As Du You was burying most of the low-grade goods underground, the Griffin Knights had arrived.
"Take these with you and, oh, this as well. Bring it back to Shaliya."
Du You directly handed over a blueprint. The Griffin Knights saluted him and attached the objects onto the griffins that they had arrived on before leaving. For these people, Du You had absolute trust.
They were all trained citizens of his own territory. Their natural souls contained the mark of the territory he'd marked, loyal to him alone. Unless there was an accident, his things would not fall into others' hands.
And after all, only a professional like himself could use this type of blueprint, plus you would need to have a territory. The locals, even if they got it, would only think it was a simple architectural plan; that too an imprecise one.