Corey, we are rooting for you. A few observations:
a) This is just SO typical of places people have "permission" for. No matter how many or who tell you "yes", it's not carte-blanche positive that any other busy-body can't STILL "send you packing". So I sort of have to chuckle when I read of someone who got "permission", thinking they are just free & clear now. Not only because this story of yours is all-too-common, but also that in their attempt to get permission, they can often-time get a "no", from a place where, quite frankly, no one would ever have seen or bothered them (ie.: the issue never occurred to the person you are asking).
b) But in this case, you DID get a "yes", and now, despite that, you are harrassed. This is exactly why 90% of my turfed park hunting is done at night nowadays. So peaceful. So serene. NOT because I think I'm doing something wrong, but EXACTLY because of what's happened to you. Like nose-picking: Not illegal, nor does it need permission, but ... we all use discreet timing so as not to offend the squeemish. Right ?
c) Because let's face it: MD'ing has ... uh .... connotations. That you might be about to leave a hole. And you will most often be on the loosing end of that debate.
d) bilder's advice of taking pix of dog crap, and asking why there's a contradiction of complaints / enforcement is NOT a good idea. Because quite frankly, the person who didn't pick up their dog's crap was probably in violation of some rule. And simply wasn't seen. It's a non-issue of how many others "get away" with something. In fact, to try to do that is merely to paint a poor picture of yourself, as if you are comparing yourself to other forms of egregious activity. On the contrary, you want to paint yourself as innocuous.
e) If you go to this meeting, do NOT bring it up, unless HE brings it up. Because it could be an idle complaint. Ie.: he may never bring up a proposed rule. He might just forget about it. And if YOU start trying to "seek clarification" (ie.: start the discussion at a city council meeting), you might just open a can of worms and swat hornets nests. So don't fight anything, unless something is truly proposed as a rule.
f) Just go at night from here on out. Or other such odd-ball times when that singular lookie-lou isn't around. Problem solved. JMHO.