For our layers, our outdoor run has an actual bottom built into it (and covered with dirt, grass, pine needles etc)....so that no predator can dig under and get in that way. I see a lot of tractors on here just being built with a wooden structure and then something over top....but no base. Our house is up on a hill - we have a large fenced in yard up here (which is where our layers live - our coop is actually half our huge shed, and we attached a super secure outdoor run for them onto that....and once they are older they will free range as well when we are outside or home). Our meat birds will be living in our lower yard - which is an acre and a half and backs onto a river. We are building them a solid secure coop down there, but wanted to make a tractor to attach to that coop (the coop will be on wheels and the tractor will be easy enough to just slide around). How do you make sure your tractor is secure without a base? Do you worry about predators digging under? Do any of you have your chickens just in the tractor at night without using an actual coop? Our birds will only be out during the day - I will coop them at night down there.