One might argue that a guard dog may be inherently easier to bribe with a treat, or cower with bluster. A trained attack cat is a far scarier proposition, given the speed, sharpness, and number of 'utility knives' they have at the ready. Also, the dog is likely to bluster and warn you. The cat, not so much. Just go for your face.

In my youth I witnessed a smallish adult puma (mountain lion) successfully harvest a nearly adult cow elk while I was hiding. I was also hunting, but focused on a bull elk somewhat further from me. It was astonishing the speed and total quantity of violence that an 80-100lb cat delivered in only a few seconds on nearly 500lbs of prey. The cat had an alomost perfect attack angle, and the combination of slash, grip, puncture, and throttle toppled the cow elk, and it ran out of resistance in very short order. I had not even seen the puma before the attack started, and I expect a trained attack housecat would practically appear out of nowhere - from behind a couch or a curtain or off the top of a refrigerator, and it would become an 'I need stitches' situation too easily.

Its probably a good thing that most housecats are pretty much impossible to train beyond 'use a litterbox' and 'stay off the kitchen counters', if even that.