You should certainly deduct $95 for the changed lock and any other costs incurred -- for example, if you fired him because your dog was neglected and it cost $100 for a vet to attend to the dog's slights. Enclose a note explaining why you are deducting the money.

You might also consider trading in your dog for a cat or two; most of them prefer to walk themselves, allowing you to avoid this mess from the getgo.