aarond raises an interesting point, and one which was used for dramatic purposes in The Girl with the Dragon Tattoo.
Stellan Skarsgaard's character lures Daniel Craig's character into a trap, simply by inviting him into the house. Once he has the reporter disabled, he tells him that he should have listened to his inner voice; that the reporter suspected he was a killer, but was too afraid of seeming rude to refuse the invitation.
On another point entirely, earlier, I recommended getting a dog. I've since received a query about recommended breeds. I don't really want to say, "get this or that" as a general rule of thumb. What I do want to say is something I should have mentioned in that original post: I only recommend dogs for people who like dogs, and who are willing to put some effort into training and working with dogs.
Those breeds that are good at actually being protective also tend to be breeds that require both a firm hand, and a lot of mental stimulation.
People who don't like dogs, or who won't work with them, should not rely on dogs for protection.