Pet DNA works great. All residents have to register there dogs, DNA is collected and sent off. If you go this route, the poop will have to be fresh, sample collected and sent off for testing. Of course the cost of testing is on the property unless you find who the pet owner is, then cost can be charged to them and based on what city ordinance laws permit. The Lease Agreement needs to include DNA verbiage and fess / fines charges that resident is responsible for. Also, rain, poop found on concrete may affect DNA testing.