Many pups like putting everything in their mouths and eating rabbit poop seems to be a delightful treat for many dogs.
You made a mistake with him and over reacted....just move on...it's not the end of the world.
Instead of saying "NO" all of the time...teach him the "leave it" and "drop it" command. With "leave it" start in the house. Have him in the house or yard with a leash on...drop a goodie or treat about a foot or so away from him...and when he goes to get it or to look at it...say "LEAVE IT" and give him a tug on the leash...when he looks away from the treat...praise him...and give him a treat from your pocket. Start without distractions and work up to doing this on walks. This is a good command when you see them eying a poop or paper or something that they may want to eat.
"Drop It" is when they already have something in their mouth...you show them a treat...and when they go to take the treat...say "drop it" and praise and give treat. You can also do this if the dog has a bone and you need to take it away...show a treat...and trade.
You could also get your puppy to carry something in his mouth while walking...it may keep him busy..so he does not get tempted to eat everything on the ground. A stick or an empty plastic water bottle or a stuffed toy is a good choice.
Have they got any obedience classes in Cyprus?
Gina