Beware of dog.

People have used dogs for security for millennia. Here's a famous mosaic from Pompeii, telling people to Cave Canem, or Beware of Dog. 

Perhaps a more useful one would have been Cave Mons Igneus, or Beware of Volcano.

As the owner of two large dogs, I have considered using such a sign. It would be useful to deter burglars. But there's really no need for a sign, because the dogs go crazy if someone comes up on the porch uninvited.

Don't get me wrong: My fuzzy baby lumpkins are as friendly as you might want. I've even composed a song about how friendly the bigger one, Tralfaz, is, because his size sometimes alarms people. Both the dogs love to meet people and other dogs. Tralfaz is such a peace-lover that he doesn't even play-fight with dogs. The smaller one, Nipper, will still do that with some dogs he thinks will be up for it. They've never acted aggressively toward a human being when away from the house, although sometimes they've regarded people with a little suspicion, and sometimes the odd bark. My wife thinks these people may be cat owners. We can't discern any other similarities, and we don't know if they own cats, but the dogs would be able to tell.

But really, our guys are very fond of human beings. So I can't say for sure they would be good watchdogs if push came to shove. They act a good game -- Nipper is totally ready to tell the FedEx man or the UPS guy off in spades. But if someone broke in, especially if we humans were out, would the guys just lick them and show them where the jewelry is?

I think probably not. Although friendly by nature and by nurture, these dogs do understand what constitutes our zone, and violators get a warning. If it was late at night, or if they were here alone, and someone came in without being accompanied by us, I do think there would be hell to pay. They say that dogs like to have a job, and absent an assigned one they will find one. Since we have no sheep to herd, no voles to hunt, I believe they see their job as Guardians of the Den, even though we did not get them for that purpose. And I believe if the chips were down, they'd carry out that job well.

In fact, a couple of weeks ago we had the driveway fixed while I was out, so when I returned I couldn't park in the garage as I normally do. So Nipper heard me coming in the front door rather than the garage door -- and as I opened the door he came running and barking like he was going to murder me. (Tralfaz sat tight -- I think he knew it was me on the porch, or maybe he was delegating to the junior staff.) Nipper has what it takes.

Anyway, we have a really, really loud security system too, so I think if the Wet Bandits broke in it would be complete pandemonium in here. I am not entirely sure any of us would survive. The police could come into a house with a blaring alarm and a bunch of dead humans and dogs. It would just be too terrifying all around. The cops might think we were hit by a volcano.