Check out this article. It' s one of the most comprehensive I have found. I can' t remember if it talks about where to place them, but if you do a search for this and make sure the time parameter is 3 months or more, you' ll find a thread that covered this subject and someone there gave good advice on where to locate them. Along trails and rub lines are a good place to start.

http://www.bowhunting.net/SteveBarty...ckScrapes.html