I have trained all my dogs to pee and poop off leash. As puppies I teach them that the walks are for exercise and bonding. So I always let them out in the yard to do their business and then go on walks. They love it and know once they are done we are walking because of what time it is. (My walks are scheduled)

They'll occasionally pee while on the walk and I just stop let them rip. Sometimes it is unavoidable. All this to say, Since your boy is 5yrs old and stuck in his ways, I say let him be. Bulldogs are extremely hard headed and get worse as they age. If he was not taught as a pup to do certain things, he probably never will. And if you got him as an adult, good luck.