If you find the balls slide off the toothpick, then first make the balls and set them on a parchment lined plate to firm up. When you are ready to dip them in the chocolate insert a toothpick or even use a cake pop stick. This may help in them sliding down the stick. You can even try using the cake pop stick or toothpick just to dip them in the chocolate then carefully place back on the parchment paper and remove stick and then let the chocolate firm. After the chocolate firms if you have a little hole from the stick, just dab some chocolate to fill the hole.