The damage is a message about how he feels
Where your dog destroys things is your first clue. Chewed door frames, scratched paint at the exit and torn blinds point to a dog whose distress is about the departure itself, often with drooling, pacing and toilet accidents from a dog who is normally clean indoors. A dog who raids bins, shreds cushions and empties cupboards across several rooms, then sleeps soundly on camera, is more likely under-stimulated and entertaining himself. The two problems look identical in a ruined hallway and need opposite responses: the panicked dog needs the emotion changed, while the bored dog needs a fuller day. Punishing either one on your return fails, because he cannot connect your anger with chewing done hours earlier.
Film a short absence before you change anything
Set up a phone or camera, leave for ten minutes and watch what actually happens. Note when the behaviour starts: a dog who is frantic within minutes of the door closing is showing you separation distress, while a dog who naps first and raids later is showing you boredom. Record how long he stays settled, because that relaxed window, even if it is only a couple of minutes, is the honest starting point for training. Note also what he targets, so you can remove or protect those items while the work is underway. Guessing wastes weeks; one short recording tells you which problem you actually have.
Build departures in steps he can succeed at
Practise the pieces of leaving without the leaving: pick up your keys, put on your coat, then sit back down, until those cues bore him. Then step outside and return before worry builds, growing the absence in small, uneven increments rather than a tidy daily increase, sometimes shorter on purpose so he cannot predict a harder test. Leave a stuffed food toy or long-lasting chew as you go during practice, and pick it up when you return, so good things attach to your departures. Keep your real exits and homecomings quiet and brief. If he panics at even the shortest step, or harms himself on doors and crates, pause the ladder and talk to your vet, who can rule out pain and discuss whether a behaviour professional should take over the plan.
Fill the day of a dog who destroys from boredom
For the opportunistic wrecker, change what the empty house offers: a proper walk with sniffing time before you leave, a puzzle feeder instead of breakfast in a bowl, and safe chews rotated so they stay novel. Close doors to the rooms with the most tempting targets, and leave him where the damage options are dull. A midday visit from a walker or neighbour breaks a long stretch into two manageable ones while his tolerance builds. Track which days go well and what filled them, because the pattern of good days is your recipe. When you are weighing whether to lengthen an absence or hold at the current step, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library.