This question is driving David up the wall

Why do some dogs after a walk rub the side of the faces on a wall etc? I've asked loads of people already but no one can give me a good answer!
Kindest regards
David Klein, Spain aka David the Dogman


Amy Hatcher, Canine Behaviourist and Dog Obedience Trainer, says...
This is a tricky one to answer as there could be many different reasons. My Border Collie bitch, Star, does this a lot after she has had a swim in the sea as she doesn't like the salty water in her eyes and mouth. She will also do this in order to mark her territory. Dogs don't have any scent glands there but it's a natural behaviour, similar to when male dogs mark the nearest bush or fence as soon as another dog passes by. There are so many reasons though. It could well be related to a happy roll - something lots of dogs do just because they are having a good time.