How about a castnet type design along the bottom? By function they have to conform to varied bottoms. If predators are a big problem it maynot be secure enough.
How many birds are you trying to house?
It's also important to choose a heritage breed chicken. These chickens are smarter and have better instincts when it comes to aerial predators.
I don't believe any solution you come up will have a 0% mortality rate, but we can always try! Just accecpt the fact that you might lose a bird or two (or 5) per season. That would be my advice, take it for what it's worth =D
In my opinion, by confining the chickens to a "tractor" and not allowing them to free range is somewhat cruel. You aren't allowing the chicken to express its chickeness to the fullest extent. Try to come up with a solution that allows each chicken to express their physiological distinctiveness! I'm now stepping off of my soap box =]
hubert cumberdale wrote:
Heavy duty netting or mesh for the side walls could be attached to a decent weight chain at the bottom. that may give you enough flexibility for what you need.
depending on your terrestrial predators, you may be able to use bent wire hoops to fix the chains in place once the tractor is at the new location.
good luck and please post pics if you get something set up.