I do both positive and negative markers with marker training. A good behaviour gets marked with a clicker or a positive verbal marker (good). A bad behaviour gets marked with a negative verbal marker (Ah!) and the reward is withheld, the dog is redirected or refocused and the chance is given again.
You can do marker training exclusively using positive only and only marking anything that you want to encourage, I pesonally like using both negative and positive because it paints a very clear picture for the dog as to what my expectations are.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010