Why does my dog wipe his paws on the grass after he poops?
After he does his business, my dog sometimes wipes his (usually rear) paws on the grass. I heard this was to spread his scent in the area, but I figured the result of doing his business did enough of the "scenting". He does this more often when unleashed in our yard than when leashed on a walk.
Why does he scrape the grass with his paws?
The behavior in wolves is known as "scrape behavior"; it is also present in their domesticated relatives.
According to Canine Behavior: Insights and Answers (Bonnie V. Beaver) the activity is commonly seen to be a visual marking, the scrapes, as well as a means of spreading scent to mark territory (as noted, dogs have scent glands in their paws). This activity happens most often in new areas, in the presence of other dogs, and in the early mornings. (Chapter 8, page 251).
It is possible to train your dog out of this behavior if you so desire. Basically, it involves distracting him immediately after his activity with something like a treat in order to get him out of the habit.