I would take him on a leash and not release him until he's done his business in an approved location and you had the potty party. I recently had to releash Freyja because she fixated on our side lawn. After 2 weeks of work she seems to have learned the proper potty location. Just in time for the sub freezing weather.
Freyja GSD- 6/21/10
Bevin (princess kitty) 08/27/07
Porsche: kitty 7/2012
Teddy (collie)- 1990-09/13/2006
Franklin (collie) 1996-06/26/2006