I have used the same trimming tool for years. Recently, I purchased the Michael Sherrill trimming tool. Here is a You Tube Video with Michael explaining how the Do- All tool works. It is precise and great for the foot of tea bowls, mugs, and large bowls.
It is sold by most pottery supply centers. Clay King has a great price on these tools. http://www.clay-king.com/mudlist.htm ($16.88 + shipping)