Some of my dogs' favorite things in which to roll:
- Dead fish (lucky us, we spend our summers at a lake full of fish)
- Bird poop, which is worse than you may think
- Another dog's poop (this just baffles me, why would they want to smell like a different dog?)
- And my personal favorite - garbage, and all that word implies.
It always helps if your dog knows the voice inflection that means "do that and forget about coming for a snuggle". It doesn't have to be "no" outright, as long as they know that extreme disapproval is there waiting.
Watch for the signs, it doesn't have to be a constant eyes glued watching, but if your dog starts to sniff the ground in a tight circle with great interest, then your need for vigilance has just increased. A hunkering of the shoulders, positioning of the body while his gaze is to one side of him, and as soon as you see that shoulder dip and his upper body start to twist, say it loud and clear - "don't you DARE!"
His body straightens, he looks at you, and you call him to you for praise in resisting the great foul temptation. And then you must take him out of the area before he decides to investigate the smell further again.