Having heard the man in charge of organising the Indian census I must say I like their approach. There is an island off the mainland where the natives are less than friendly. In fact it's been made a no-fly zone due to the spear throwing the planes started. Come census time the officials approach the island but not too closely. They throw from their boat into the sea coconuts and others items of interest to the locals. Once the tide brings the items in, the natives come out of hiding to collect everything. When this happens the officials are ready with their camera's and click away. This is how the islands inhabitants are counted. Great. Not sure how they decide what religion they are though.