But then I would be like most other posters here on biggerpockets that bark hard but no proof.

Most tenants who have dogs (I say most because there are some that do not fall into this category) do not take care of the property as if it were their own and when you add a pet dog (or dogs) in that equation things are dirtier because of the dog feces and urine, the dog tearing things up (scratching doors and walls) and the annoyance of leaving the dog alone and it barking constantly affecting the neighbors (this is more of an issue with apartments not houses).

When I showed up the dog barked, but no one answered. 

It cannot tear the place up, poop where it wants to, attack other people or pets, or bark its head off.

They have a dog which is lease does not allow, wonder if that can help me, neighbors complain it barks all night.

I did have some rather strong objections, usually from BoA, but the bark was worse than the bite!

I use canine, feline, animal, 4 legged furry things that scratch, spray, bark and soil.  

@Dan C. most people like dogs (as long as they don't bite them or bark all night).

Whoever is the owner or person legally in control, have a lawyer send a bark and growl letter sent to him.Sir,Your contract has legally expired and your refusal to remove the lockbox is an illegal trespass on my property.

I would explain that I enjoy having them as tenants, but the situation with the pets makes it impossible to continue the lease.By the way, if they want to stay you should "steel" yourself for the innevitable, "...we'll train them not to bark...."' or "....we'll cage them when we're out and that will solve it....".