Put the coop half of the tractor on a small trailer chassis. make the run so that it moves to wherever you have towed the coop, and then can be attached to wherever the pop door is. 
That way the coop will be secure overnight. Less likely to be an attack by digging in the daytime, but could happen even then.
That way the coop will be secure overnight. Less likely to be an attack by digging in the daytime, but could happen even then.
