Go to the automotive store and get a tire patch kit. This is not a tube patch kit. Rather, there will be a thick, strong patch in the kit which is specifically for patching tires. These work pretty well.

Next, you have to fill the hole in the rubber part of the tire. Even though the patch will support the damaged threading from the inside, you want to keep debri from entering the cut. I use Shoe Goo, just because I have not found anything else to use.