Came across this study from Wisconsin early 2000s. They compared standard electric fence versus crisp protection dogs contained with invisible fence. I found the description of dog choice highly amusing

"On 13 July 2000, the fence
containment system was installed and two
female border collies were deployed within
the 1.4 ha field. One of the border collies
was extremely fearful of loud noises (i.e.,
thunder, gunshots) and was replaced after 45
days with a male Labrador retriever mix.
The Labrador retriever mix caused damage
(i.e., digging holes and urinating on plants)
and was a nuisance by barking incessantly
and demanding human attention. The
Labrador retriever mix and the remaining
border collie did not roam the containment
area and failed to keep deer out of the field.
These dogs were replaced by a third female
border collie and a male hound mix in
September 2000. The new dogs also failed
to patrol the containment area and confront
wildlife. Therefore, they were removed in
January 2001. Dogs that were not directly
observed to confront and chase wildlife were
perceived to be ineffective and were
replaced. None of the dogs in 2000 were
acceptable by our expectations. However,
crop damage was reduced to only $116,
taking place in soybeans specifically planted
to test the efficacy of the dogs (Table 1).
Most of this damage (97%) occurred before
13 July, the start of the study and the
deployment of dogs.
At the beginning of the 2001 growing
season, a male purebred Siberian husky and
a male German shepherd mix were
deployed. The shepherd ran wildly, jumped
on people, and was removed immediately.
Conversely, the Siberian husky actively
patrolled the containment area and was
observed chasing deer from the field. On 20
July 2001, a female Siberian husky,
Malamute mix was deployed. She also
actively patrolled the area and chased deer.
After the two Siberian huskies were
established, no damage occurred in the 1.4
ha field for the remainder of the study. Both
of these dogs continued to work the farm
until June 2004 when the male Siberian husky died of natural causes. The female
Siberian husky, Malamute mix continues to
roam the field."

Kinda like they were just grabbing whatever dogs they could come up with through the local craigslist. lol

Opinion:
Border Collies want a herding job, they'll protect what they're with but just to roam ... naw.
Labrador Retrievers, c'mon what the second word in their name. Want them to go retrieve a deer for ya? The labs I've had would be more apt to go out and try to make friends,
German Shepherd ... someone let this poor dog down, he needed proper training for anything. A guard dog who demands attention is apt to point out the good stuff to a thief.
The Huskies actually surprise me. Avalanche is a good alert dog but Sky (or Sasha) neither of them would have been what I consider a guard dog.

Al - it's not so much that they are a guard dog - it's their pretty drive that makes them suitable. And they don't tend to bark to alert. The primary reason i was able to get Ami is that deer are a huge problem here and hubby adores his rhododendrons. Deer were eating them terribly. Not since Ami came on premises! First night i walked Ami around the perimeter at midnight, several feet napping under the pines leaped up, shocked, looked at each other as is to say - "who put the wolf in the Sharaf buffet?!!?" Then they all bolted

Kasper would chase the crap out of some deer if they came into an area where he could get to them. I have 9 that actively live and sleep in my field by the house and it drives him nuts he can't get to them. He got a rabbit a while back that foolishly slipped through the back fence. So far his kill rate is a baby 'coon, copperhead snake, rabbit, and multiple mice. Don't think he would take down a deer but he would have a thrill chasing them.

My old dog who was a pitt/lab/st bernard/collie mix was a heck of a guard dog. No training necessary. If it hadn't been introduced to him by us it didn't come through that fence. People included sometimes.