Hm. I can only comment on Bentonite Clay (?) We use Bentonite Clay in the concrete industry as a concrete pump primer (it slicks the inside of concrete pump truck lines to prevent clogs and allow concrete to move easier through the system). It is generally not used in structural concrete as it rises to the top of the concrete and does not mix with the concrete.
I don't know how this would assist with digestion issues in a dog besides "slicking the lines," but I'm open to hear someone else's opinion on it that have used it before/know more than I do. (I just read something online that the clay acts as a magnet to attract toxins though.)
(Kind of like "Alpha Hydroxy" - found in high-dollar age-defying skin cream - is another term for a type of acid used to remove concrete off of tools and trucks)
I tried that for Indy once. It was part of a two part thing, it was probably a decade ago. I know nothing bad came of it, but I don't remember anything stellar, either. She was real messed up at the time though. I remember something about the process was difficult (if you waited it gel-ified or something like that), but I don't remember if it was the clay, or the other part that I also can't remember!
I did think of trying it again years later, but never did.
I always thought of it more as drawing bad stuff out rather than coating the intestines. I also think that for long term use, it can pull out minerals and such, but I'm pretty iffy on my knowledge base here!
they put this clay in Nature's Variety Instinct dry kibble dog food. other dog foods in the industry are breaking into adding this. nature's variety claims that if there is ever a mold problem in the kibble it won't kill the dog like when diamond had that horrible mold recall. the clay actually absorbs toxins in the body and helps with anything entering.