I think any dog can be a good guard dog, i think a lot of burglars would decide there and then whether to carry out the job if they saw the dog that was waiting inside, what i mean by that is if they saw a chihuahua im pretty sure they would just go about there business as usual where as if they saw a rotty or a pitbull then they would possible think twice ?
There was a case a couple of years ago in the UK where a guest was holding a party at his manor and he had 2 rottweilers who lived outside (trained guard dogs) that patrolled the area around the manor, during the party a guest left her baby unattended and the baby wondered outside outside to play with these dogs, the girl ended up being killed by the dogs.
Now i understand if you are going to be holding such an event the dogs should be kenneled, however who in there right mind leaves a baby unattended, these are the stories that give dogs the bad reputation they have today.
Another very similar case also including a rottweiler, a mother and father left there 7 year old daughter babysit there 2 year old daughter whilst they were out, only to come home and find ambulances and what not outside there house, the baby had been killed by the rottweiler! WHY because the 7 year old girl when into the kitchen where the dog was crated and took him our placed the baby on him so she could ride him like a horse. lucky they were not both killed.
To summaries i think any dog is capable of attacking a burglar or intruder, what damage they cause is a different story.