If you start pitching your dogs as so dangerous and easily provoked that they might maul a trespasser, and that you might be helpless to stop such an attack, you had best consider the consequences of that. First, absent postings about your dangerous dogs, they might be deemed a hidden or concealed danger such that you could be liable for their attack on a trespasser. Second, with such postings, such a claim could put the cost of your liability insurance through the roof as you're effectively giving away the farm in the event that they bite somebody who has permission to be on your land - your stating that know your dogs have a propensity for extremely vicious, unprovoked attacks. You're also putting the dogs in danger if they bite somebody as, in the event of an attack, animal control is much more likely to treat them as vicious dogs that pose an unreasonable danger to others, as opposed to treating them as pets that made what might be an anomalous attack on a trespasser.
The place to start truly is with your insurance company - both in terms of making sure you have adequate coverage for your property and, if you're going to stick with the "attack dog" idea, that you have adequate liability insurance for dog bites.

