Neighbor Rental Property Tenant Issues

[Byron Bohlsen]

Hello, 

I have a rental property with a neighboring rental property. The neighbor tenants are leaving garbage on my side and letting their dog **** in our yard. 

Curious if you guys know how this is handled, tenant to tenant, Do I talk to their tenant, or should I try to track down their landlord? Or just call the city and go from there? 

Thanks.