H.W.
We use Rental Services, Inc. in Denver to do a background check including credit, criminal, evictions, and employment. It is not fool-proof or a guarantee, but we have only needed to evict one out of the five tenants at this point, and they just had a run of bad luck job, health, and family wise that depleted their resources. Unfortunately, they also smoked in the house and weren't supposed to, so we incurred more damages on that. We increased our pet deposit after that, too. We ask for $300, $150 is refundable if all damages and rent is paid, but there is also $15/month pet rent that is non-refundable in addition to the other $150. We called apartment complexes, and this was rather low, but we feel it covers us sufficiently (at least at this point in time).
You can contact an attorney to help you recover costs, or a collections agency. The nice thing about the collections agency route is that there will then be a record on the person's credit report that signals the next landlord (assuming they do a complete background check) that there were issues with their prior rental (yours!).
I am really sorry you had to go through this. It is NOT fun. You can also just say, "NO pets" if you don't want to deal. We've had numerous people look at our places that did not have pets. People with pets I think tend to look to the smaller landlords specifically because they don't charge as much pet deposit and pet rent. Call around to a few apartment complexes and ask about their pet policy. It's an eye-opener!
Good luck. Call if you want the name of collections agencies. I haven't used one yet, but have interviewed two that were recommended to me.
H.