if you have central heat remove the register and hide stash/paraphernalia in the duct (i used this when i was a kid), you just have to be careful with the screws. a false electrical outlet is simple to cut into the wall using an LV remodel box, it's only big enough for stash and small pipes but everything is securely hidden inside the wall (i used this one with very nosy roommates and landlords, they didn't even notice it was fake when i moved out). in plain sight works on the unsuspecting, but parents aren't usually that.