Prior to putting in our 4x4 posts for our picket fence I put in about 4 or 5 inches of water at the bottom of the hole. I then will take about 1/3 of our first sack of our ready to mix concrete. I will pour just enough in there so that we can start mixing the water and the cement together to form a really good tight firm footing for our 4x4. Now that we have our 4x4 posts in our hole we are ready to pour our ready mix concrete into our hole mixing it with water. While I am doing this I will continually check my plumb line and my level to make sure things are plumb and square.