Ive tried the whole 'no' in a stern voice. Shoving toys in his mouth when caught chewing something he shouldn't be, Different chews, Kongs, sprays, segregating etc etc etc
He's chewed through the pissing freezer cable, shorting all the plug sockets in the process now.
What, The, Bloody, Hell do I do with this dog????
Previous owner should of been bloody honest about him 
I love him to bits, he is a great dog, but this chewing lark is his downfall.