i think you’re being very sensible to try and put a stop to this behaviour especially if people are beginning to label him – poor boy !!
the first thing i would do is suggest that you dont let him offlead again until you have basic control and management in place (e.g. “leaveit” and a recall at C5) this way you are preventing him from being able to do the behaviour you dont want 🙂 hope that makes sense !
i know it seems cruel, i’ve been there myself with Bonnie and numerous foster dogs but it is by far the quickest method of getting your “leaveit” / recall really reliable and fluent. once you have this then you could think about working on greets etc … once that is done and you are confident either letting him greet or managing – then will be the time to think about puppies 🙂 it’ll be much harder to do this once you get the pup because you’ll have to leave puppy behind everytime you train stan and leave stan behind when you take pup because otherwise he’ll teach pup the stuff you dont want 😀
based on my experiences, i would think 3-6mths – longer if you have no ‘stooge’ dog to get this reliable and fluent enough to be thinking about a baby poopi – does that help ?