I am repairing a section of my deck fence. I need to install 8 decorative fence posts but I can't nail them straight in from the top because the fence is too complex. I'm thinking about renting a nail gun and nailing the top of the posts to the horizontal board from underneath at a 45 degree angle. My question is will this knock the post out of position when the nail goes in? Or does the nail gun shoot so fast the post won't move?