I like watching my dog dive into the sand pile in the backyard. I kick a tennis ball into the sand and he of course dives after it getting sand all over himself and in his mouth. Most of the time he just digs around the ball...just digs...ball doesn't even move...really making his latissimus muscles work. I just watch and kick the ball whenever he brings it back for about 14-20 minutes. He'll return the ball maybe 7 times or less within the 14 minutes...he just keeps digging....and digging. Makes me happy to see how happy he is for something so simple. It's rather funny when he discovers another ball that was buried and he'll sniff it and chew it trying to decide which one; he usually trades to the buried dirty one if he wants the ball kicked immediately after (totally gross which is why I kick the ball with old shoes).