[KSL]

We just recently moved from a condo to a house, which has a (small) fenced in back yard and a lot more space than our condo.
DH and I are thinking we'd like to get a dog. (I had a dog before l married DH, a border collie/lab mix I adopted when he was a year old-- he was a great dog but was several years old by the time we had DS, and he was not adjusting well to having a baby in his space so we re-homed him to dear friends where he had an awesome life. We also always had a family dog growing up.)

Anyways, we want to get a dog for a few reasons:
1) DH wants a dog who will bark/alert us if people are at the door or outside house. I would also feel better having a dog here as well when I am home on my own with kids. I don't mean like a vicious watch dog- I just mean a dog that will bark and alert me if someone was ever coming into home or was at front door.
2) I think DS is ready for some more responsibility and would really enjoy having a dog to play with. I know we (DH and I) will be doing the vast majority of the work with the dog, but I think DS could handle feeding/providing water and he loves to go on walks with my dad's golden retriever so I think the walks would be a nice family thing to do together (plus I have fenced in backyard so we can easily let dog out between walks).

So the most important qualities for us in a dog are:
1) good with kids
2) large enough so that the bark would deter unwanted guests/act as protection

Ok. So here's my question. Given the above, and the fact that we want to adopt a puppy (I really want a puppy no matter what the breed, so that it is used to DD especially and we can train it to be tolerant of kids from the beginning), what breed would you get?

I am seeing lots of Labrador Retrievers and Boxer puppies in my area on PetFinder, and actually some Lab/boxer mixes, and those breeds are appealing to me. Any others I should consider?