What protects me from being wrongfully fined from my apartment leasing office?

Things like that are impossible for the apartment complex to prove unless they have a photo.

Yes, they need proof and if they charge you, you'll have no choice but to tell them that if they insist on fining over no proof, you'll have to sue them in small claims...as a judge will require proof.

However, they have no legal right to fine if it's not spelled out in your lease.

I feel your pain. I have this idiot on our HOA that lives down the road from me and a little upset after I refused to go on a date with him...ever since then, I constantly get letters about my grass and garbage when is all BS.

I would stop by the leasing office with the letter and ask them how they know it was you since you ALWAYS clean up after your dog. Have a very calm and quiet conversation with them and just find out how they determine who does and does not pick up after their dog. If they are relying on complaints from other residents then how can they really prove it was you? Anyone could make a call and say you didn't pick up after your dog - after enough complaints you might get evicted. If it happens again (and you have been picking up after your dog constantly) then you're going to have to start wondering if you made anyone mad in your complex and might have to confront them directly.