Choosing the right breed...

Hi everyone,

My 6 year old son has been asking for a dog of his own, and I'm having some difficulty coming up with a suitable breed.

I live in a single family home with a decently sized, fenced back yard, with 6 foot tall wooden fences.

The biggest obstacle I face are the two dogs that live with us right now: my wife's 9 year old male Chihuahua, who weighs about 12 pounds -and is pretty easy going as far as Chihuahua's go- and a 7 year old male Lab/Terrier mix that was my mom's, he weighs about 22 pounds, and is a docile, sweet pup.

I'd like the new dog to meet the following criteria:

-pure breed, open to a mixed or cross breed
-medium to large in size
-good with children
-good jogging companion (for me)
-halfway decent guard dog
-low wanderlust, if at all possible
-young or young adult (so I can jog with him/her right away), but open to a puppy
-most importantly, one that won't kill both of the other dogs

I had my heart set on an Akita, a Rhodesian Ridgeback or a Black Mouth Cur (or all three!), my son loved those breeds as well, but they don't seem like good choices if I am to keep the Chihuahua alive. I've read that Chihuahas don't fare well with Hounds, large Terriers or Spitz-type dogs.

I also have two parrots, which I imagine would rule out most of the sporting group breeds as well?

So, indeed, this seems to be a tall order. Any guidance would be most appreciated.

My thanks in advance