Barking Pyranees

I'm hoping that someone here can give some suggestions on how to teach my
Great Pyranees not to bark...or at least to reduce it!

KC is a 14 month male, non-neutered Pyr who has perfected barking ! Luckily
we live in the country with no neighbours to get upset, but the barking is
driving us crazy.

Some days he is great, hardly no noise from him at all, and yet at other
times he will constantly bark with no obvious stimulus....I guess something
is bothering him but it's not obvious to us.

When outdoors he is tied up with a 60ft long chain that gives him pleny of
space to roam, when indoors he has freedom to go where ever he wants.

No matter where he is he will bark, indoors, outdoors, you name it.

Things we have tried:

Spray water in face
Muzzle
Put him in his crate
Keep him indoors
Keep him outdoors
Electric shock collar

so far nothing works. The barking is so bad that the next step is to send
him back to the breeder, because it is driving us crazy.

Hellllpppp.