We have a large one--not the kind with the flap, but with two plastic doors that part in the middle when the dog wants to come in. We installed it right in the wall so that it goes into a storage room, and I like it better than the version with the flap--you can actually lock it, using the plate and key that come with it. One thing that you'll need to look out for (and I almost blew it) is to get it close enough to the ground so that the short legged ones can get through it easily. We ended up having to put some dri-tek down so Pearl could hop in and out easily. I can't comment on the critter factor, though, because it leads out to an encloesd run, not to an open yard. I've heard stories of critters coming in through these things, but in the many years we've had dog doors, some of them leading to the yard, I've never seen it happen.
[ February 02, 2006, 06:59 PM: Message edited by: S. Hall ]