Tree bark powder has a lot of fans in the raw feeding group I belong to, but I don't know anything about it. I'll have a look and see what I can find.
I keep pro-kolin in my dog first aid kit and have used it with success, but it's not something I'd use on a regular basis. I'd be wanting to find the cause of the problem.
There's a product called Bionic Biotic that's intended for daily use and meant to be very good at helping keep the gut healthy.