No matter what breed you chose, you need to do a lot of background research;
Find out all about parents and grandparents
Ask for some references from the new owners of previous litters.
This should give you some idea of what are the strong and weak points of given dog line.
What other animals you have/ what exactly you need to guard?
Do you have a "big" predators or small?
My little Chihuahua is making the most rambling and its the first one to charge into woods, if she only smells something nearing by.
My Great Pyrenees is quiet, not barking, but he is still a baby.
I can see that hes got potential; the way he listen and behave.
I noticed its the Chihuahua who is teaching him some undesirable acting, such picking eggs or going pass our property lane.
So, the lesson is; make sure that your new dog wont follow the bad manners of your existing/older dog that is if you feel that your existing dog has something bad to teach.
I assure you; they learn and follow the elders very quickly!