Some cats will carry out unprovoked attacks on the dog. This is most likely feline territorial aggression. "Unprovoked aggression" is always unwelcome. The recommended treatment for the cat in this case is "leadership petting" intended to lower the self-perceived status of the strong willed personality cat.

When the dog is threatening, the cat will need to exhibit "defensive aggression" to get the dog to back off.  This is entirely appropriate. An even better alternative would be for the owner to follow the protocol below, and to interrupt and scold any dog who chases the household cat.

There is another more serious potential motivation. Some dogs have a higher than usual "prey drive " in addition to their chase instinct. As a result, if this personality dog catches the cat, it well may result in murder.  The fleeing cat certainly does not want to wait around to find out which motivation is behind the chase.

Protocol For Most Cases Of Canine Aggression Toward Cats

• Prevention:  Introduce species to each other during the early socialization period prior to puberty. The earlier in life the species are introduced to each other the better. Interestingly, it does not have to be the individual animal. Introducing any kitten to any dog, and any puppy to any cat (as long as it is gentle) works.
• Set up the first meeting between dog and cat so that a chase will not occur. (e.g. dog on a leash) If the dog has previously chased the cat, take steps to prevent that from happening again. Don't allow a "habit" to develop.
• Prior to the meeting, work on the dog's basic obedience Instructions to reestablish leadership and control.
• Begin the introduction by feeding each on opposite sides of a door, or with the dog tethered.
• When both are relaxed and bored with sniffing, introduce them on opposite sides of a large room. The cat should be inside a portable kennel, or up high enough so the dog cannot get there.
• Reward the dog with food treats in exchange for compliance with obedience Instructions.
  Gradually move them closer to each other as each seems relaxed with the cat still in the kennel. Go slowly, it may take several days. A slow introduction saves a high time involvement correcting a problem.
• Once they have met, only let the cat loose in the house when you have the dog on a tethered or on a leash. Feed the cat while dog is around, to set positive association with presence of dog.
• If a chase starts, give dog a scolding or collar correction. Praise any gentle sniffing and friendly interaction.
• Let the dog see you gently greeting the cat and petting it with a calm demeanor. Model what you want.
• Feed the cat high enough that the dog cannot access and steal the cat's food. (e.g. on a counter or fridge)
• Similarly, keep the litterbox behind a gate or inside an area the dog cannot access.
• Medication is a last alternative. The goal would be transient during behavior modification.