For example if I constructed on my property a wall 20 feet tall, my neighbor will surely object, and he'll be right, he has also the right to enjoy the surroundings.
If you constucted a wall 20 feet tall on your property it wouldn't be the neighbour objecting it would be the planning authorities , I havn't worked there for some time but the old rules over there limited you to 1200 mm at the front and 1800 mm at sides and back , unless you could prove to them that you had a very good reason to exceed it .
Though unless the planning rules over there have changed you could plant them bloody awful cypress lelandi(sp?) to give you what is effectively a 20' + wall in a very short time .