How to train my dog to eat slow

We have a 1 1/2 year old male golden doodle, we got him at 8 months old, he came from a home with children and 3 other dogs. We do have one male husky about 2 1/2 years old but the two dogs get fed in their cages both morning and night time. The problem is that my doodle will scarf down and swallow his kibble whole, we’ve put obstacles in his bowl and scattered food on the floor and slow feeders down for him but it makes no difference. When the chances have arrived he will literally eat the entire bag of dog food, how do I ACTUALLY TRAIN him to slow down, I don’t want tools or band-aid fixes. No “scatter food on the ground” “use muffin tins” etc these don’t do anything I’m looking for real training techniques Also have gone through changing his food for different nutrients, he will literally poop himself in the kennel every night. The only dog food his body will adjust to is what we have him on