tell him off when he pisses indoors, with my lurcher shaking him by the scruff works, but when you've got to go you've got to go could you hold it in if you were really desperate,i would let him out for a piss every half hour maybe or maybe its a bladder problem if like you say it goes straight through him have word with your vet.
As for the dogs diet, as many of here will tell you raw is the best option, Rabbit (not boiled though) wood Pigeon, pheasants, Venison, beef, chicken, pork is thought to carry worms so it is best to research into that, and any chopped veg you would like to add. all