Chewing it over. And over. And over.

I have a three-year-old Collie cross and he has a habit of stealing items to chew. He doesn't do it whilst I am out of the house so I think it may be for attention. He does it when I am in the room, or in another room, and started after we had had him for about six months (aged two).

He has off-lead walks and games of fetch every day and he has his food in treat balls, Kongs or scattered. He has lots of toys and chews (stag bars/rawhide) but gets quickly bored. I've tried swapping for treats and other items but I think that has made it worse and am now putting him in his crate when he does it. I remove what I can but he will take cushions off the couch, clothing and newspapers.

Any ideas as to the best way to stop this behaviour? Should I just persevere with the crate/time out? He has also growled a few times when I have tried to take things from him.

Many thanks,

Jack's mum