Ned--There is an interesting book called "The Archaeology of Ritual and
Magic" by Ralph Merrifield New Amsterdam Press 1987 which may give you clues.
The index doesn't show beads or blue beads but there is at least one chapter
on Household magic--"Charms against witchcraft"--which discusses various
charms buried in foundations and walls. There are pictures of some great
Bellarmine witch bottles and their contents.  Also, Gullah Root Medicine in
Coastal SC uses conceptually similar charms--bundles buried under the front
step keep witches from crossing the threshold, and so on. I haven't heard of
beads in this context though. While  I don't believe that every blue bead has
the significance that the HA article might indicate, certainly some do. If  I
found them buried at the four corners of the house I would certainly
interpret them as you suggest.  Carl Steen