Once he gets it call him back. Give him a treat when he returns with the twig or ball. Remember this should not require you to unzip your pants. Have him fetch two beers and give him one beer. This seems to work.
Dogs have a tendency to lick their personal parts.
If your dog licks another dog's personal parts he may be gay. There is no method of training to break this habit. This is useful to get off the phone with an extended talker. Having your dog bark is a good excuse that you have to let him outside to relieve himself. Use a treat to teach him.