Been down this road as well. Had a bitch that had ate 'something' and had a blockage. Xrays could see the mass but could not identify it/correct it without surgery. We were spending some time with her prior to surgery and she squatted, strained and yelped and when she cut loose it was handfuls of garden mulch. If one knows something has been chewed up and swallowed soon after it happens the peroxide will get it back up. If it is a day or so and it is into the intestines the mineral oil will work if the piece is small enough to pass. Time is a huge factor here because if it is a lot of little pieces they get packed together in a twist or turn of the intestine and it is pretty much surgery or death when that happens.
Best of luck to you and the dog. Time is critical in these situations. EWO