Sgt_Kickaxe - 3:20 am on Jan 3, 2013 (gmt 0)

Redirecting doesn't get rid of the urls. What you want is for your indexed urls to return their content and for every other url possible to return a 404. I realize that's difficult when its a category page as you mentioned but you could force a 404 on any url ending with a backslash(or vice versa if your urls append one all the time).

404 is the only virtual surefire way to get Google to stop weighing a page against your domain. If a url has EVER had content on it Google will indeed crawl it for eternity.