Dog exercise pen? Is it safe to tractor in one?

Hi,

I was tractoring the chickens in a dog exercise pen while I was out weeding. I put bird netting over the top with clips to hold in on and u shaped landscape fabric brackets to hold the pen in place. Has anyone tried doing this successfully?

I have a separate tractor, but it is in another section of the yard and it is awkward to get it across the cobble stones. I wanted an easy solution to have them around me. Since I was out with them I thought they would be fine, but the neighbor is worried I will lose one to a hawk. She had a hawk land on top of her tractor last week while she was in the garden. She chased it off. Does the bird netting protect them from hawks at all? The chickens would never be in it over night or any thing like that, but I am sure I would go in to the bathroom or get the phone sometime.

Thanks for the help.

Edited to add a pic