if there are any pet shows near you with a royal canin stand, they often give out slow feeding puzzle bowls for free
our border collie got bored with his though and left half of his food (wasn't such a bad thing as he is on a diet)
but mum ditched it in favour of his old bowl as "he'll starve"

a (then) 29kg border collie will starve having not eaten around 60g of food?
yeah right!
i'm not going to be very helpful with advice regarding messing in the house - our boy still wasn't completely clean until he was 3.
it always seemed to be because of necessity though, and he always chose the same tile in the kitchen.
he's an odd one. never known a dog do that for so long then suddenly just stop.
Re-trumping though, aren't the X and potato foods usually suitable for this kind of intestinal distress?
Burns Pork and potato or Harringtons Salmon and potato come to mind.
harringtons state on their packaging that they reduce flatulent odours, but obviously it depends on your choice of feeding.
i would perhaps look into the possibility of a wheat sensitivity first.
and try to cut out treat/human food as much as possible (plain chicken i think will be fine though, you can also dehydrate chunks of beef in the oven to use as treats)
my dog had a terribly sensitive stomach when he was younger, It can be difficult to pin point what is causing the distress sometimes. with him it appeared to be that his puppy food was too rich for him, then another food he was given was just.... i'd say it wasn't even good enough for the bin. and some of the treat sticks mum was giving him just didn;t agree with him. (and still don't today) Thankfully he grew out of this a bit though, and has a much better constitution these days, but he still can't stomach oily fish.
it's horrendous though, not knowing what to do. there were numerous bouts of diarrhoea within a 6 month period with him, this combined with adolescent eating habits making it difficult to get him to eat at all left him incredibly skinny, but still happy and active as ever.
hope you find something which agrees with him a bit better, nothing worse than rancid dog toots!