Growing into impulse control

When my dog and I walk, I like to keep things interesting for him. Keep him mentally stimulated by varying routes and even simply walking the other side of the street. Tonight during our walk, I was remembering back when he was about 5 months old. He was driving me insane or to the point of exhaustion or something. Anyway he was learning what things were by putting them in his mouth. He would pick up trash or rocks or eat horse poop and I would almost contantly be saying "drop it" while we walked. I thought he would never stop and he did, eventually he would leave just some of the less interesting items and now he leaves 99% of them. He made me think of it tonight as we walked right over some horse poop without a glance, I told him "good boy" and felt proud that we have come so far. I notice it in other things too. He has learned what is what and doesn't become so obsessed or insistant about things, I can get him away from most smelly spot with a simple "let's go" I do still use "leave it" when smells seem too interesting for him and if he leaves it I typically praise him and guide him over to what he was smelling and say "ok" so he may sniff as a reward. He seems to back off and leave it if he thinks he may get a chance to smell the item afterall. He also used to go in my closet to "steal" socks or whatever smelled good to him at the time and now I find if I tell him to stay out he does pretty well at leaving that stuff alone too.
Don't lose faith in your pup because the rewards are forthcoming and oh so great!