I am in the process of putting up a wooden fence (standard 6 foot high, three 8 foot sections), books call for the post to be in the ground ½ of the fence height. Lucky me, the soil is real rocky and has remnants of old concrete from previous fences. Digging with gas driven auger was an ordeal, and I got the holes 2 ft deep. If I poured concrete around all posts, not just the end ones, could I get away with just 2 ft holes? Thanks.