Obviously he was hiding it from Federal confiscation. Did you look inside the ductwork? There are probably more guns hidden there, along with lots and lots and lots of ammunition. A spacious place to hide ammunition is the furnace's heat exchanger, until the heat is turned on. Also look above any suspended ceilings. Is there an old bomb shelter? How about between the wall studs -- did you look there? Some folks, knowing that Obama is going to personally come to confiscate their firearms and short arms, have taken to burying them (inside an appropriate container) in the backyard and then having cows pee all over the place (the iron in the urine foils metal detectors, or so I'm told).

The best way to get the yard dug up is to anonymously contact the FBI and tell them that commies have buried guns there for The Revolution. Of course, if they DO find any guns they'll keep them, but you could sue to get them back.