Any vets? Anyone tried dog nappies?

[Stillmonday]

Our 13 year old lab has bottom problems.

We've resorted to her wearing a dog nappy at home to reduce staining and also closer monitor her bottom! She poo stamps when she sits down, it's just a smear but still gross!

We've changed her food which looks like it might have made a difference however there's still a small brown mark in her nappy when we look close at the end of the day. But would that be normal or should it be 100% clean??