I will probably get flack for posting my dog pen as a "day tractor."
My urban yard is completely fenced with a 6 foot block wall and 6 foot gates so stray dogs are not an issue. My only worry is hawks over head and that is why I use bird netting on top. I never leave the hens in it over night. They go back into the coop at night because we have raccoons around. I would not recommend this for open yards or overnight accommodation.
We are not allowed to free range in my city so this is my solution to get them access to most parts of the backyard the tractor cannot fit. I use my tractor occasionally for a couple of hens, but I really prefer the puppy dog exercise yard because it fits in the oddly shaped parts of my garden and in the pathways of the veggie beds. It folds up really small and I store it when not in use.
I found a couple of my pictures with her play pen in the back ground.
Here is her speckled sussex pullet perched on the edge. You can just see a little of the plywood top. She just lifts it and sets it off to the side when she isn't using the pen.