Thanks to everyone for the great comments, insights, and suggestions. A couple 
of points and requests for additional information:

Kirsten: Most of my research material pertains to the eighteenth, nineteenth, 
and twentieth century in the United States, but occasionally I come across 
earlier references. Also, there have been several witch bottles found in the 
U.S., but once again they are more recent.

Dave: Brian and I are already in contact, but thanks for the reference. As you 
already know, his work is pretty much contained within the U.K., whereas mine is 
in the U.S. I occasionally pick his brain for ideas and sources. J

John: I’ll have to check out the Pennick citation. Thanks. Do you happen to have 
any citations for scissors as apotropaic devices, particularly under thresholds 
(other than Merrifield)?

Mogg: Do you have any citations for this information? If so, I’d love to take a 
look at them.

Rose (Pitch?): I don’t know much about modern magic practioners, as I’m an 
archaeologist so my focus is more on the historic and material aspect. But I 
have come across some general descriptions of blacksmiths as magical. I know of 
one paper that looks at the ritual role of the blacksmith in Africa, but I can’t 
seem to lay my hands on it at the moment. Let me know if you have any other 
citations for blacksmiths and magic. I’d be very interested to look at them.

Cody: Interesting observations. My knowledge of mezuzahs is limited, so I would 
be interested in any academic articles concerning their application. I’ll also 
check out the links you posted. Thanks!

In addition, last night I was surfing ebay (when I should have been sleeping) 
and came across this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220588749247&ssPageName=STRK:MEWAX:IT 
I’m not 100% that’s a horseshoe motif—it could just be a stylized decorative 
element—but the concept is interesting. Unfortunately I don’t have an extra $200 
bucks lying around.