Hey, Georgie, this isn't my corral, just a photo of one of the many projects on my list (I will edit this post to reflect that). However, it looks to me like this person uses t-posts at both ends of each pallet to secure them, but you could use more traditional building methods if you chose.
If you like our blog and would like to help support what we do, please feel free to donate any amount to help keep us going! Our goal is to use this blog to help care for the animals. We will let you know how your donations are used. Thank you!