Here is a great article that explains it far better than I can. There is also a book out there called "Mine!" that is really good.
http://www.clickersolutions.com/arti...ctguarding.htm
alexbnieto I don't mean to pick on you. I've just seen how the wrong type of dog can react to that type of correction. It's just too dangerous. A lady in puppy class with us had to put her first dog down because it object guarded and she was told by a trainer to use corrections for it. Many dogs guard because they fear you will take their stuff. By using a physical correction, they learn that their fear is justified! Sadly, her dog got worse, not better.