While dogs in various sizes can provide deterrent as well as protection, please make sure you consider the inherent responsbility that goes with a dog.

First, you need to be willing to care and provide for this animal. These are social animals so it isn't fair to dump it in the back yard. They need to be cared for, trained, played with, perhaps given a job. It takes time... It is a commitment.

Second, for a larger, more protective dog, you need to protect the dog. An incident where the neighbor's kid gets bit may cost your dog it's life (and get you sued). While dogs have successfully lived with humans for a long time, they are not people and do not understand the world in the same way.

Third, you need to protect the neighbor's kid.

-john

(for small yappy dogs, typically only #1 applies. they tend to get a lot of slack because they don't threaten people)