Great. Thanks for the additional information. I really appreciate it.
It absolutely sounds like you have the perfect example of a terrier on your hands. This breed of dog, possibly more than any other breed, is infamous for their energy, hyperactivity and habit of getting themselves into trouble.
I do pitbull rehabilitation and have spent many years learning about them...and one of the most important things to know about pitbulls is that they are very prey driven...which made them great for working with livestock (which is what they were initially bred to do), but unfortunately it also made them very likely, unless well socialized and trained, to chase smaller animals/other dogs as well, and some dogs are simply more prey driven than others, and it's important to remember that any self-respecting dog, regardless of the breed, if not socialized will act out in this fashion ..this is as true of Chihuahuas as it is of pitbulls or pitbull mixes.
There are many, many great sites that can give you a ton of information about the history of pitbulls:
Pitbulls have a long and wonderful history that demonstrates that, in the right hands, with an owner who understands the breed and knows how to handle them, they can be amazingly wonderful companions who do great with kids, other dogs and even smaller animals.
My favorite suggestion in cases like this is to suggest you enroll him in a obedience class. It will give him a chance to become better socialized in a controlled environment with other dogs who are also learning how to interact with one another, will give you and King the chance to bond through working together, and will teach her the basic rules on how to get along with other people and animals (I know that currently he has no problems with people or small dogs, but if her behavior with the catsis prey drive, it could transfer to people if we don't get it in check).
The next thing you're going to need to do with your guy is get him on a strict regimen of exercise. I understand that you have a pretty significant injury, so obviously this will happen once you're healed, but it's important to always remember that terriers NEED to be exercised every single day, and I'm talking more than a quick walk around the block. A rambunctious breed like yours needs a couple miles a day to drain his energy and keep him from getting into trouble because he's too wound up.
You may want to consider using something like a Gentle Leader (www.gentleleader.com) on your walks rather than a prong or traditional leash and collar. This is a head harness that goes over the nose and behind the ears. It makes these big strong dogs easier to control because the logic is that if you control the head, you control the dog. I use it with my rehabilition pitbulls and really like the control it gives me over them.
Secondly, you might want to consider clicker training your dog. This involves buying a 'clicker' which has a little metal plate in it. You press the plate and the thing clicks, then you give the dog a treat immediately. Soon, the dog learns that the click brings a treat and will usually drop whatever they're doing in order to come get the treat. You can see more about clicker training here:
This isn't an easy thing to change, but I think that with a lot of patience and some fine tuning, you can turn his prey drive into something better.
I hope this helps.