Oh dear… the old eating faeces dilemma! This is unfortunately a common issue and it certainly can lead to illness.
Different species stools can carry bacteria, protozoa or parasitic worms that can cause problems when ingested by your pooch. It is important to have a good parasite control regime at home with a dog that likes to eat faeces.
Some dogs will exhibit this behaviour due to nutritional deficiencies or other gut disease, so it is worth while chatting to your local vet about this behaviour, your little mate’s diet and general gut health before assuming it is a behavioural issue. If at any stage you notice that he is not himself, or has any vomiting or diarrhoea, take him straight to your local vet for treatment.
If you have the all clear as far has any health issues are concerned, the only thing left to do is train your cheeky mate to avoid eating anything off the ground whilst on a walk. I will say this is VERY challenging and takes lots of persistence and patience. To start with I would suggest keeping him on a leash for all walks. If he goes to lick/eat anything (don’t just focus on poo) say “Yuk!” loudly then call him over to you with a treat in your hand to give him straight away. Eventually he will associate the “Yuk!” with going to you for a treat instead. You can then progress to walks off leash. There are other techniques that a dog trainer or veterinary behaviourist may suggest. Unfortunately, for a lot of dogs the reward of eating faeces can be too great to overcome with behaviour modification training… If this is the case, keeping walks on leash to control what he gets into, is likely the only way to avoid the behaviour…
I wish you all the very best of luck! Keep us posted with how you go!