Just bury in the bush .. do NOT lose the GPS coordinates and make sure it's not in an area known for gold deposits. Just use a PVC pipe.. forget the bullshite about tarnishing.. ensure you wrap it a few times in good plastic. Put in PVCpipe, screw on the ends.. bury at least 3 feet.. then bury a can or two (soft drink) at two levels above your PVCpipe.. JUST in case someone comes along (LONG SHOT) with a detector.. the detector goes off, they find the first can, they check one more time for safe keeping, the detector goes off and finds the second can.. they then give up.. if you are really paranoid, you ca get a CCTV camera that is batery operated and runs off a SIM card.. it will capture video and photo from a built in sensor, and then email you a photo. Its like an alarm essentially. Anyone goes near your stack, you will at least be alerted. Cost? Maybe couple hundred for the camera, and another $00 or less per year for a SIM with data pack. You don't need to capture people near your stack, what you want is to be alerted so you can get there, or call the cops or your neighbour or whoever. It is an alarm!!!