To get through that cocker hair, you are going to need a two speed clipper. Me, personally, I prefer Andis over Oster, I find the Oster's to be bulky and not comfortable in my hand. Cockers have pretty thick hair, and any clipper that has "trimmer" in the name isn't going to cut it. Shell out the money for a quality set, and there will be a huge difference in the quality of the cut. Be sure to groom a CLEAN dog too. A dirty dog will just leave track marks everywhere.