Besides Debby's site, I found this site about the "pasture paradise" track system as well:
http://thenaturalhoof.homestead.com/paddockparadise.html This person's website is almost in blog form and I'm really interested in reading it, as she says she has, previous to going to a track system, had her horses dry-lotted because she has an IR (Insulin Resistant) horse who had foundered. Right up my alley / situation. -- Renee M. in Michigan