When he barks excessively we have been going out and throwing water at him. It has quieted him quite a bit.
Please don't ever do this - or other punitive things that dogs can't reason. As was said, you are only teaching him that you coming out to him means bad things for him and could be escalating his people problem.
I think a trainer to the home is a great idea and am very relieved that you have found a positive trainer who will use a clicker. I trust she will teach you how to avoid using all negatives with him that fail to show him what you want him to do.......
Putting him outside all day is not optimal - dogs are pack animals and isolation is the worst thing for them. Working dogs who work outside all day are focused on a job at hand (mental stimulation) and stay with their flock, owner, etc. Simply being banished in a backyard is punishment.
Patrick gives good advice in my view - I have never met this breed that wasn't aggressive with strangers on the property - this is the breed. So if there are people coming around, putting him in a quiet room (that signifies calm, peace, and positive) is a good idea.....not some place that will be construed as punishment. Also, when put in this place, he should be given a stuffed kong or something to occupy him, keep him focused and stimulated and positive.
Think Positive! All things positive.