People leaving dog poop on common areas at condo...breaking ociation and town rules..how to train owners?

Most of the people that live at our condo complx are very responsible dog owners with well trained dogs, and carry their own baggies. The ociation is against putting up "doggie pick up stations" like at parks, uming the responsible people are OK, and it won't cure the irresponsible ones, and will add unfair extra cost for own non-pet-owner residents. We've tried notices in our ociation newsletter, they've ignored. I put up "curb you dog" signs in my window, they left fresh big poops below the sign. I put the sign in my car by the fields, they keyed my car. I've talked to the township, but they said we need pictures and "evidence" in order to press charges. We talked to some of the people personally, only to get nasty comebacks or lame excuses of "bad back" or "bags in the mail". Finally I tied up baggies to the courtyard lighting and trees, but this could get me in trouble for putting items in common areas. Any way to train these owners NICELY?