Never had this problem before!
We have 3 dogs, one of whom is a 4 month pup. He's going through the teething phase and he's a big chewer - mainly of our skirting boards and boiler cupboard.
The dogs are rarely left alone except for on a night and brief periods in the day - I think the chewing is happening at night. We have nylabones, stuffed kongs and stagbars all of which he loves - but still he chews.
The areas are drenched in chew deterrent from pets at home but they're making no difference to him.
I realise that the easy answer is to crate him, but DH is anti crate (don't get me started 
)
We never catch him in the act to be able to tell him off.
Has anyone got any brilliant solutions?