They would work but I suggest making sure u have them in the ground about a foot or put some sackcrete I. The holes to make sure they are sturdy. The post we have are actually old landscaping post (they are treated.) I think they are around 4 ft apart.
We have the 2x4 for ours we have 4x4 post though. No problems yet but they are young and we let them out in the evenings to graze in the yard when we r home.