I'd go for a maremma. In fact I already have...
They don't stray like Pyrenean mountain dogs, so long as you regularly walk the boundary with them. They'll then chase off any intruders and come back when the intruder las left. My dog revels in chasing away crows and deer, but never chases them too far.
Ensure that you get working dogs, not show dogs. Depending on the size of your property, you may want to get quite a few of them, so that some can stay with the flock while the others (generally the males) go off to investigate the intruders. This is useful for the coyote situation mentioned above.
They're also very intelligent and if you take the dog to investigate a disturbance (say the dog was in the house), it will look at you and wait for a signal before dealing with the trouble. This seems´to be totally instinctive.
But they do take two years to grow up and can be little bastards when they're young. They don't take orders very well compared to most dogs, due to their independent nature.




