Just having toys does not mean a dog is not bored. Alleviating boredom in dogs means that you are also interactive with them and the toys, giving them adequate exercise for the breed (and Border Terriers as with most terriers, are higher to high energy and often need more solid exercise in the form of walks, sports, games, etc than most people realize). A tired dog is often a better behaved dog. Also, regression in training is perfectly normal in dogs. Go back to basics, put the trash bins out of reach when you are not home (I put mine in the bathroom and shut the door) to alleviate temptation and then wear him out before you leave the house. These will help keep him from trash diving!