Why do dogs roll in vile things like decaying trash?

A couple of hypothesizes come to my mind and these could explain why do these lovely creatures act in this way. One of them is to cover up their own smell and thereby make it more difficult for their preys to identify them and runaway from them. As a matter of fact, some hunters have adopted similar techniques 

A more down-to-earth way of interpreting this behavior is that they do it to show the rest what they've found. Dogs like those kinds of expressions or communications. Believe it or not the best hounds like to roll in vile things, and if we consider dogs have hundreds of millions of smell receptors when we only have just a few millions. I'd say it's something one should think about and consider.