my son built this wonderful mobile coop. He used lawn mower wheels. The first time we moved it we discovered the coop is far too heavy for those small wheels. We are thinking of adding larger wheels (such as the back tires of a riding lawn mower), two on each post, one on either side of the post. Or, add an axle. The chickens love their coop and so do I, but I need to be able to move it around. Can someone help? An inexpensive solution would be most welcome!