This is one side of the dog pen. It measures 25 feet long (as do the other 4 sides). The fencing itself is 6 feet high. See all the rocks at the bottom of the fencing? The fence is lined inside and outside all the way around. Some rocks were place in low spots to keep the dogs from digging their way out, but the rest are there just for a place to put them.
Oh, if you look really close in the center of the picture (in front of the doghouse entrance, you will see a rock. It and its twin (hidden by the doghouse) were left in the dogpen because they are so big they cannot be moved.