I have three kids under 4 years old, so I'm in the thick of behavioral correction all the time. While I have had no reason to spank my kids yet, I don't think it's something I would take off the table. We use a lot of Time Outs, Taking Away of Prized Items and Count Downs. Children are very frustrating, they know how to pick at every last nerve. While I would never use Violence to correct violent behavior, I think it only reenforces the violent behavior. I can see where a spanking to correct seriously dangerous behavior to themselves or others could be used.

Also, be consistent, and follow through any threats you make. The latter has worked very well for me. My kids are now teens and preteens, and threats of having prized possessions temporarily removed still work as well today as when they were toddlers because the kids know I bloody well mean it. Consistency is vital to children, otherwise they will not be able to anticipate the consequences of their actions.