Rodney

Used to work in an office building -- a fourplex with a central staircase open to the outside -- and the guy in the office opposite liked to bring his rottweiler to work. Thing damn near rammed through the glass doors to get at me a time or two as I came up the stairs. I'm uncertain about the combination of Rottweilers and kids. Like somebody else said, it may depend on the individual dog, but I would play it safe and get a breed which, while protective, has more of a rep for being kid-friendly.

In your case, the dog is more of a deterrent than anything else. So you might be just as well off with a noisy, barking dog (or two or three) who's moderately tough rather than the toughest dog possible. If they make enough noise, nobody'll ever go over the wall and they'll never have to fight anybody. Labs are good, German shepherds are good with kids that they know as most K-9 cops will tell you.

With any large dog, of course, proper training is a must. Be sure that they get it.