Cats to dogs:  Before the cat is introduced, test the dog out for severity of predatory aggression.  Some breeds have a tendency toward severe aggression; terriers, Rottweilers, Greyhounds.  If the dog appears to be safe around cats, teach the dog to sit and stay using food treats.  Make sure there are high, safe places in the home for the cat to escape to if necessary.  Advise owners to start with the cat in a completely separate room.  Owners can practice sit-stays outside the room.  When the dog appears to be calm, the door is opened a crack and the procedure repeated.  The cat can be fed a meal when the dog is in view, to prevent running.  Finally, allow the two to be together, first with the dog on a leash and then, when safe, loose.  Make sure the cat always has access to safe places that the dog cannot get to.