I guess you need to evaluate if he gets anything more out of it than just having garden time.
Towards the end with our old american bulldog, it used to take 45 mins for the walk I do now with
our young presa in 15, but she was always up for it. It was only her last couple of weeks with cancer
where she couldnt be bothered at all and just sat in the garden for hours.
Otherwise, if its just pace, then walk him on his own.