Okay so here it goes, they make some metal detecting shoes or GPR (ground penetrating radar) shoes.  Though they may need someone with rather large feet to hold the equipment required. <br>Then create disguises as structural engineers, the ones from the council that come around every so often to check that the building is in safe conditions. Apon finding a reasonable signal that could be the penny, open a case against the building that says they must fix something.   I suppose they could plan this in advance and make some kind of corrosive formula to spread near the location of the penny resulting in some visible damage thus convincing the proprietors that there is genuine work needing done. <br>orrrrrr, detonate the entire building, raize it to the ground or whatever and then sift through the remains.,(reply>), or, mark the spot of the penny on GPS once found with the GPR and then dig under and up to the penny.