What should I do?
Answers:
Talk to the landlord. If that doesn't work, file a complaint with the animal control or sheriff's office, whoever handles nuisance animal complaints in your area. You don't have to put up with this sh!t. Literally.
Other answers:
move
move
Call the landlord and complain. Animal feces is considered a health risk.
call the land lord and throw them under the bus!
What i would do is go and tell your apartment manager and ask if he/she can do something or anything about it.Tell him how it smell and how far the smell is going into your apartment. You might want to ask him if he can go and inspect the neighbors apartment! To make sure the dog is doing ok and to make sure he has it clean in there!
File a complaint with the SPCA.