New Outdoor Tortoise Pen

I have recently build a new outdoor pen for the torotises in a leftover spot of out garden. We had some extra wood left around so I just nailed them together in a rectangle shape. Unfortunately, the wood in not dug into the ground like it is suppose to be so they have been trying to dig out. To solve the problem I just put a few wooden stakes in the ground where they were digging. I also threw in so bark and rocks just so their pen isnt completely bare. I am bringing them in at night just because I dont want any racoons to mess with them as I dont have a top for it. During the day I usually put a box on top of half of it to give them some shade in the afternoon as it is been rediculously hot here in CA. This pen is only temperory as I moving back down to San Diego in a few monthes.