Ohhh, wow, one week. It took my beagle - now deceased after a long life (bit too short for me, sigh!) - several months to get it down. And he was a very bright dog!! (There were days I was ready to tear my hair out by we persevered - those are the puppy year, lol)
This dog may have been in a situation too where was scared. Also, he may be scared in a new situation. So you may have added complication. Never scold him - that will just make him more afraid.
Here is an article that may help you:
http://petplace.netscape.com/article....asp?artID=797
http://www.soyouwanna.com/site/syws/...og2.html#para2 (may be less helpful since it is for younger puppies)
Good luck! I am sure some of those than operate rescues can give you great advice.