Potty Training Regression - need training help

[Bizeebee]

We've had our hound for a bit more than a year now, but lately we've had more and more trouble with messing in the house, despite a year of being pretty well potty trained (he can even ring a bell to go out!), so we're kind of at a loss for the best thing(s) to do. Since the holidays he's been peeing and now pooping more in the house (despite thorough enzymatic cleaning of affected areas), always when we're out of the house for work or errands.

Last winter he was experiencing some medical issues that caused peeing in the house, but he's been on meds since spring and that particular issue (being unable to fully empty) has pretty much resolved. He'd had a few #2 accidents along the way, but it always when he'd broken into his food and gorged or had way too many treats the day before - the cause was never a mystery. So, of course we've had his urine checked (no sign of infection/crystals) and his stools are great, he's on maintenance dose of moxidectin (no hooks for quite some time), and since figuring out that he can't do chicken his gut has been healing up nicely and poops greatly improved. It's also pretty clear that he is able to hold it (#1 & #2), because he can make it overnight and on the weekends he is one lazy hound. All that to say, that with the exception of a minor ear infection (treatment in progress) he's pretty healthy.

With a pretty clean bill of health we're convinced this is behavioral, but dont have a great idea of how to deal with it, other than the obvious "praise when he goes outside". We give him lots of chances to empty before we leave and he's never alone for more than 4-5hrs, but swear to dog this guy can create waste from thin air. He still rings the bell and does his business outside during normal turnouts, and since it is happening when we aren't home there's no great way to catch him in the act and do anything about it at the time.

If this is some kind of delayed separation anxiety - he has no reaction when we leave the house - how do we deal with that? Besides the first few weeks of settling in, he had never exhibited anything close to SA - no messing no destruction no panicking when we left. He hated the crate so we never bothered with it and he never really needed hard core Alone Training.

Any tips from anyone with experience with this kind of backsliding are more than welcome