I have looked through several of the older threads on this topic, but I still haven't found a good solution to my problem... My husband is doing a great job building our tractor. It is a 6x8 A-frame that he decided to make using cedar so that it would last. The problem is that it is no where near done, and it is already really heavy (for me at least)... I had him extend the handles that we will use to lift it so that it will add an extra 2' to the moment arm and give me a little bit more of a mechanical advantage, but we are still going to need some heavy-duty large diameter wheels. We have a lot of 200-300 pound predators (bears and mountain lions) that could easily tip it over if we elevated the coop off of the ground for the wheels, so I'm not sure how to get mobility without also getting the lift. Pictures of what you have done on your coops would be greatly appreciated!