Sounds like a wise decision. Sometimes I wonder if I'm getting too lax with this free ranging thing, we've been letting the chickens loose for several years now, but thankfully we've had no issues. The tractor's a good idea, that way they can get at the grass when they've scratched up everything in the coop. I was very surprised at the state they managed to reduce the back of our garden to at first, there is quite literally not a blade of grass there anymore.

The only thing growing is nettles, and the chickens even eat the seeds of those.
Interestingly enough, the neighbourhood cats are terrified of our chickens. At first we thought they'd be a problem, but the chickens have scared them off many times, quite funny. But you're right not to take chances.