I used telephone poles for all my pens. One even has all telephone poles for the line posts. Just make sure to use a good creosoted butt ends for your corners and dividers. All the ones that didn't have a good butt end I painted good with a bucket of roof tar, They have been in for 16 years and all are still good shape. Built a pen for something else a long time ago and used good creosoted butt ends. That was over 30 years ago all corners are still good a few of the line posted finally rotted off but I don't think I used the roof tar on those at that time.