I remember hearing once about odd things found by renovators within the walls of houses.
Like mice and insect nests--things that would happen naturally. We found an ancient mouse nest behind the wall that covered the chimney. A nice, warm place to sleep after raiding the kitchen.
They never lasted long after we moved in, though.
I remember one humorous English newspaper story that renovators had come across a "Letter to the mice" putting the rodents on notice to "Leave forthwith and never return!"
Especially interesting are items intentionally put within walls by superstitious people wanting to thwart bad spirits, spells, and things of like nature. Water-filled, corked bottles were common in the New England area during the early settlement period. Witches were very real to those people. Effigies, containers with hair, pins, herbs or spells thought to contain magical powers were placed in the walls during construction.
Shoes are common things found in many ancient houses and barns, although the symbolism of shoes escapes me. They are usually stuffed into the rafters or built into chimneys . (Chimneys were thought to be convenient entrances for witches.) Mummified beef hearts (???) were another common thing sealed in chimneys . No one seems to remember the symbolism, though.
I also recall stories about the hiding or burying of things under the front door step. Probably also to serve as a barrier for evil entering the house, and I can well remember horse shoes hanging on barn and farmhouse door lentils as well as talk about three rusty bent nails buried at a threshold.
Hex signs are still painted on barns and houses in the Pennsylvania farm country.
A research paper written in 2007 and found here: http://www.crossingthethreshold.org/welcome_files/Microsoft%20Word%20-%20Soc%20of%20Consc.pdf discusses many items and symbols used to protect a house.
I have a potter friend who, every year takes one of his best pots, walks out to the end of his dock on a local lake and quietly slips it into the water. He's thinking of future archaeologists. Vikings did the same things with axe heads as an offering. And, well, he lives in Minnesota. : )
In Arizona if you can't sell your house right away, bury a small statuette of St. Joseph in the yard. There is some argument whether it should be the front or back yard; whether St. Joseph should to upside down or upstanding, facing the street or facing the house. Poor St. Joseph.
I still have a chance of slipping something between the insulation and the dry wall of the kitchen. Hummm, what should it be? Think I'll go out to the studio and have a little look.