A loose fence post can not only affect the integrity of a fence as a whole but can also make a fence look uneven and unappealing to the eyes. Fence posts will become wobbly for a multitude of reasons, such as poor installation, ground settling and from being knocked loose by a car, tractor or other outside force. Fixing a loose fence post will maintain the rigidity of the fence as well as maintain the fence's uniformity for a very long time.
Dig around the base of the loose fence pole as well as underneath it with a shovel. Use a level to position the fence pole so it is level and plumb.
Temporarily brace the fence pole in the level and plumb position by nailing a scrap piece of wood to it, level to the ground, across the hole of the ground laying flat. You may want to use a piece of scrap wood as your brace for the fence post. Keep the brace from moving by placing heavy objects over both ends of the board.
Mix the quick-setting concrete according to the instructions provided on the bag. Pour the concrete into the fence post hole and create a slight slope from the fence post to the ground, so that rainwater will not be allowed to settle at the base, rotting the post over time.
Recheck the fence post's position to make sure that it is still plumb and level, and make adjustments if needed. Allow the concrete to dry fully, and then remove the temporary wood brace.