Guy goes down to the dog kennels to get himself a guard dog.

The dog breeder says he has the ideal dog for the job and he brings it out for inspection. It is a little bigger than a poodle and looks about as threatening.

"Get outta here! That's no guard dog, couldn't scare a mouse!"

"No" says the breeder "It's a real killer. Let me demonstrate. GUARD DOG! The chair."

With that the dog transforms into some kind of psychopathic beast and totallly destroys the chair.

"Wow! That's really something. Can I try it out?"

"No problem, feel free." says the breeder.

"GUARD DOG! The table."

Same thing, dog rips the table into pieces, the guy is well impressed, buys the dog and takes it home to show his wife.

"What on earth have you got there?" she askes.

"It's the guard dog" he replies.

"Pppppffftttt! GUARD DOG my arse!"

ouch