Our miniature dachshund had the same problem. We went to Petssmart (any pet supply store will work) and purchased an actual dog diaper. I think we paid around $5 for it. It's made out of different material so you're able to wash it. I didn't know if you already knew about Petssmart so I thought I would help.
Using vinegar on your scalp really does help with dandruff. I use to have it bad and I would use this maybe once or twice a week and it worked. Of course, shampoo after with something that smells good because the vinegar does not have a pleasant smell.
