I would first try to figure out what kind of hunting pressure the contiguous lands to his is receiving. Unless he purchased a few thousand acres the deer are not spending all their time on his property. If he has food plots, agricultural fields, mineral licks or good trails a few good trail cameras would be the best indicator of his deer herd. I expect that the non-pressured deer were easier to see and now that they have hunting pressure they are more nocturnal. They are probably still in the area.