William likes to hold on for ages until he's absolutely bursting and then goes in the garden, squats and pees a lake
. He was the same even as a puppy and I sometimes worry that it can't be good for his kidneys
About 2 or 3 times a year he'll have an accident indoors (major clear up of flooding because he's held on for so long) but it's because he's refused to pee in the garden last thing at night or before I've gone out somewhere, so I have to be very firm and stand in the garden with him when he's like that and make him stay out there until he has a pee. First thing in the morning I make sure he has a pee before I feed him his breakfast and I won't let him sneak back in the house until I've seen him pee. No such problems with Louis, who sprinkles pretty much every plant, tree and pot in the garden at every opportunity
. It's odd really, because William was so easy to housetrain and Louis was so slow to learn.
I think you would know if Riley had an infection. Will had one a few months ago and he had a couple of accidents in the house on consecutive days and was also desperate to dash out and pee frequently in the garden.
Does Riley cock his leg and mark when you're on walks? If so could you get a friend's dog to come into your garden and pee where Riley has been trained to? Sounds daft, but it might encourage Riley to start peeing there again. If not, can you stand in the back garden with him on lead in the peeing place first thing in the morning and try waiting until he goes and then really praise him? Maybe that would get him back into the habit again.