After years of monitoring and trying to be "bin manager", I have found that in-ground bins work best for me. I still have about 16 plastic bins going, because I sell worms and bins. I have all kinds of possibilities set up to demonstrate, how it can be done, in many different kinds of situations, to people who come here to build bins. I have a hole-in-the-ground bin, which was never actually a hole,( never got around to digging it). I just put food scraps on the ground, covered it with leaves, and waited for the worms. They did come and brought all their friends. That bin does not have any cover, so it is a free for all. I don't really care, so it works. I have built some cinderblock bins, that do have hinged lids. They are just dry stacked over some hardware cloth, in contact with the ground. I grow most of my herd in those bins, so the free lunch is closed to other large creatures. I do not monitor any of those outdoor bins very much, and I think the worms and all other decomposers are much happier with me just dumping the buffet in and leaving them to their business. They know what they are doing, so..YAY!
Here is a link to the images of my cinderblock bin and 1 shot of the hole-in-the-ground: http://photobucket.com/albums/y209/redhen/projects/