To make the groove, reposition the fence so it is a little farther back from the bit. Then, close the fences. (If the fences are in the exact location you need them, you can use them to cut the blind groove as well. But, if not, follow these steps for another way to stop and start the cut.
Use a board to locate the start and stop locations of the bit. Place a board against the bit and make a mark on the fence at the place where the board touches it (Image 1).
Use a straight edge to carry the mark up the face of the fence so that it will be easy for you to see (Image 2).
Repeat the steps to make a marker on the other side of the bit. Use the marks to let you know where to start and stop the cut. Rather than pushing the board into the cut, slide the board down the face of the fence to start the cut.
For safety, wait until the bit stops to remove the board from the router table.