[Jespah]

Rupert is a maniac roller - Riley did it all the time too. Rupe grunts and smiles and goes crazy! Jemma does it as well. I often have people walk past me chuckling away as I have two dogs at the end of their leashes rolling and grunting away. I think it's a combo, like you do, of pure happiness and some scent marking.
I find Rupe rolls in a different way, like it's all business when he rolls on something nasty to pick up it's scent.