I know very little about service animals, but I am sure the training includes ensuring that the animals aren't going to be destructive- the last thing a person who needs a service dog needs is an animal that is making messes in their home and chewing up walls or whatever.  

I wouldn't think pet messes and chewing would be allowable.  

The only thing we had to worry about, is if the cable in the wall gets chewed up by a creature, etc.  

Itemized Repairs and Related Losses to get unit back to move in condition: Replace living room blinds – dog chewed up $145.35 Replace bedroom carpet – dog urine $375.89 Patch nail holes, repaint $18.00Total Repair Cost: $539.243.

They even complained on one that the local chipmunks and squirrels had eaten their plants in the garden (complete with photos of chewed plants) - and the remedy they sought for each of these filings was termination of the lease.

., but should give you a few things to chew on.

Labs are puppies until they're about 3 years old, and they chew on everything.  

@Eddy Dumire any breed of dog can be violent, it really all depends on how the owner takes care of them and trains them. if your concerned about the potential damage from pets, you can do one or a combination of these:1. charge an additional deposit to allow the pet (along with security deposit)2. charge a slightly higher rent (ex. additional $30/mo )3. only allow pets under a certain weight4. don't allow pets at allI'd typically lean more toward no pets at all, but I've made exceptions in cases where the flooring was at a point where I was debating on replacing or not. you also need to pay attention to people with pets as some will scratch or chew on doors, walls, cabinets, and other things. this goes beyond just dogs and cats too, so I'd at the very least take a deposit for any pet. 

I once got a call because there were squirrels in the attic and one had chewed through the ceiling and fell on a tenant while she was working in the kitchen:)

Cats can also be destructive--this one had chewed the quarter-round on the baseboard, for example.