Poop eating habit

My male shih tzu is a little over 4 months old and has the disgusting habit of eating his own poop. Both the vet and trainer say it’s common. It seems to be purely behavioral, he has no parasites, has good nutrition and no reason to be bored or stressed, we spend lots of time with him playing etc

We try to remove his feces quickly but he’s learned to do it super quick too so he snatches a piece before we get to it. Yuk!!!

Any words of advice to get rid of this behavior?