First thing I can say is I feel for you, been there done that. Second, he still is only 5 months old and he will get it so you have to be patient which is easier said then done. Third and what worked well for me, is to have a word or phrase when you go outside with him to pee. "Lets go pee" or whatever you want and also have a treat with you. After he takes a leak, praise the heck out of him and give him a treat. Won't take long until he figures it out. Labs are chow hounds and love treats!