Cão de Fila de São Miguel... I'm in love!

 They look like teddy bears! OMG!

I'd think the major problem would be people throwing themselves at your dog.

A lot of these rare, guard breeds are rare for a reason - they aren't entirely well suited for suburban lifestyle because they still retain the true temperament. It sounds like you have a good resource offering help in researching them though.

I don't know about the rounded crop but PyrSheps get a straight across crop - sort of unusual.  

Acaldeira

They are rare because the breed needs more divulgation, even in my country they are fairly "rare". There are lots of countries in Europe using them as working dogs because they are extremely versatile, they can be used as a guard dog, a herding dog, a personal protection dog, agility, you name it. The dogs are very wary of strangers and they need a proper socialization since early. I'm planning on getting one myself by the end of this year since i want a dog for canicross and bikejoring and i want to expand the knowledge people have on our breeds. Regards, Adolfo Caldeira Here's a well known Portuguese breeder that has a website in fairly basic english with some grammar problems but you get the point: http://www.azorescattledogs.com/

 Like I said, some of the rare breeds don't tend to fit into modern suburban life as easily. Not saying they can't be great dogs but probably more than what the average family needs for a pet.

As a trainer, I don't recommend these breeds to pet homes at all.  The reason is that, as AgileGSD has said, they are often more than average families can handle, and when the family isn't prepared to raise a working breed correctly, these dogs can often become aggressive.  These are serious working dogs that are often very territorially defensive, and can pose a significant threat to visitors they don't know.  Because they are cattle dogs, their modus operandi is similar to other cattle dogs - bite when the cow won't move;-)  Even with exceptional socialization, some individuals will be still be very wary of strangers, and dogs sometimes make wrong decisions, so the owner lifestyle is important to consider very, very strongly.