DannyboyLeather - yours looks more like an
Irish Staffordshire Bull Terrier .....a great, stout dog!
I wish I had one!!!
raindog101 - you're getting lots of good advice here....but, ahem....it's a bit "all over the map"...
There are a few websites out there that can help you figure out what dog breeds to start with...(note the careful wording....no one breed will be the perfect breed...but there are probably several very close...)
Here's one I mess around with all the time:
http://www.glowdog.com/bestdog/
(you'll need to take time to learn how to use the settings properly - and make several "best dog" lists...not just rely on one...I still go back and revisit this site)
You can get breed-specific info here:
www.dogbreedinfo.com
And you can search your local rescue shelters here:
www.petfinder.org
Now...some random thoughts:
guard dog = will protect property (may or may not bark)
watch dog = will raise the alarm, but under threat of injury, will back down
Most dogs are some mixture of both....but several breeds swing more toward the extremes. Most terriers make great watch dogs....while mastiffs, dobermans, shepherds, AmStaffs, StaffieBulls, Rotts, Schnauzers...make great guard dogs.
Try and decide which 3 of your list are the most important and go for those.
"Dominant" is not necessarily breed-specific...it depends a lot on the dog...and also on its owner. Even the lowly chihuahua can end up being very dominant if it is catered-to too much (you become servant instead of master)...or if it was just raised that way. You just need to show it who's the boss and you'll be ok.
Granted, some breeds are more stubborn/independent upon being told "I'm the boss"...but problem-dogs aside....most dogs will eventually submit.
At the shelter, avoid any dog willing to sit in its own feces....(don't feel sorry for it...just walk away).....also, avoid any dog that pees when you pet it (can become a fear-biter).
Also generally speaking...

....bigger dog = more food...don't know if that matters.
Since your property is unfenced....you are probably going to want a breed that is owner-dependent (such as a lab, retreiver, bird dog, etc.) and not a wanderer (any hound) or an independent dog (any terrier).
Here's the reason why I say "pick the top 3 most important traits":
Border collie - energetic, working dog, med size, easy to train, smart.....but sheds, is somewhat hyper, and may or may not attach to the kids (they prefer to work).
Lab - good "family dog", great w/ kids, med size, not hyper....not a good guard/watch dog, not as easy to train, health problems, overeats, sheds.
Doberman Pinscher - great guard/watch dog, trainable, low shedding, med size.....but aggressive, not as good w/ kids, excitable (not really hyper though).
Golder Retreiver - great w/ kids, med size, trainable, decent watchdog.....but sheds like crazy, won't last 20 miles/day.
Know what I mean?