How strange, I have been thinking off and on about this despite not knowing very much about dogs, and scanned down the forum this morning and suddenly an image of a Puli popped into my head (I was actually thinking about Poodles first), opened the thread and found someone else had got there before me. And then realised how old the thread was!
I have very limited experience with gaurd dogs, so I can't really help you there, but have had considerable experience having dogs around to help keep varmints out of the chickens and other critters on the farmstead. We've had everything from Heinz 57 mutts to some highly pedigreed dogs, some were exceptional some weren't worth the food they ate. The key to our success is to find a dog that wants to please you, then make that dog your constant companion until he old enough to fend off the boogey man outside by himself, even then when your outside the dog needs to be your shadow, he has to understand that the entire farmstead is yours and everything on it is under his care. Now it's a lot more complex than that but at the same time it's that simple. Research traits of dog breeds, very important learn the body language of dogs, watch the dog whisperer he's very good at pointing out doggy body language, if you know what the dog has on its mind it makes training so much easier. I noticed you could be leaning toward a jrt, most I've dealt with made very good barnyard dogs, one of the drawbacks to terriers is some of them have more heart than good sense, which means they're not afraid of much and can be difficult to call off before leaving your property, I've known people who have lost them to coyotes because of it. IMO they seem to do better working in a team of 2-3. If you want any other info I'll be happy to answer as best I can.