Treated 4- by 4-inch lumber posts are one of the strongest and most cost-effective means of installing fence. But, digging the holes for them is one of the most grueling physical labor tasks known to man. Installing fence is rarely as simple as it should be, and running across concrete slabs is a common challenge. There are several ways of dealing with the challenge. Using galvanized post brackets and tapcon-style anchors simplifies the project considerably. You'll need a drill heavy enough to punch a hole in solid concrete and a galvanized 4- by 4-inch post bracket.
Measure the position of your post carefully. Typically, fence panels meet in the center of the post. Use a string to mark the line of the fence and a tape measure to get the correct spacing between posts. Mark the four sides of the post bracket using a carpenter's square. Make sure that the post is set square to the fence line.
Place a 4- by 4-inch galvanized bracket squarely inside the marked space. Using the galvanized bracket as a template, mark the pilot holes for the tapcon-style concrete anchors on the concrete. Double-check your measurements before drilling the concrete.
Use a hammer drill with a 3/16-inch masonry bit. Set the bit in the chuck, and tighten it well. Wrap a piece of masking tape around the bit at 3 1/4 inches to mark the correct depth. Drill the pilot holes in the concrete. Keep steady pressure on the drill, and allow it to do the work for you. Once you finish the hole, use compressed air to blow the concrete dust from the holes.
Use a drill with the recommended screw tip to drive the anchors. Set the bracket in place, and drive one anchor into each hole. Snug the screw down tightly. Avoid overtightening the screws to prevent stripping. Use 1/4- by 3-inch tapcon-style concrete anchors.
Place the treated 4- by 4-inch lumber post into the bracket, and stand it upright. Use a post level to check for plumb, both front to back and side to side. Attach the post to the bracket with treated 2-inch deck screws. Use a screw for every hole available.