Look for tools which have spur-like wheels on them. These tools will perforate the wall with thousands of little dots, so that the dif can soak in.
[header] How to remove wallpaper with the dif method [title] Perforate the wall. [step] It is important that you do not " score " the wall, as this will damage the wall and cause the paper to come off in small strips. Specialized tools are available at your local hardware store.