Your dog slept through your working day at 5 months old. At 11 months old you come home to a chewed door frame. Or a message from a neighbour about barking, or food you left that was never touched.
What changed
Usually nothing dramatic. Adolescent dogs are awake more, they need more to do, and any skill goes soft without practice. If your routine shifted at some point this year, your dog has had less practice at being alone than they used to.
There is a harder possibility worth naming plainly. Distress at being left alone is a welfare problem rather than a phase, and it does not usually improve on its own.
Tell the two apart tonight
Point a phone at the door and leave for 10 minutes. What happens in the first 5 minutes tells you which problem you have.
Bored: a slow start, a wander, some chewing of something interesting, then sleep. The chewing is aimed at objects, not at exits.
Distressed: it starts within 2 minutes and does not settle. Pacing, panting, drooling, barking or howling on and on, scratching at the door or the window, and food left untouched.
If the video looks like the second one, stop here and book a veterinary appointment before you train anything.
If your dog is bored, tonight, 15 minutes
Feed one meal from a stuffed and frozen toy, given only as you leave the room. The toy appears with your absence and goes away when you come back.
Give your dog 20 minutes of sniffing on a walk before any stretch alone. A dog who has used their nose settles more easily than a dog who has only used their legs.
Leave the house for 3 minutes, come back in without a greeting, and sit down. Do that 4 times this evening, at 3, 5, 3 and 8 minutes.
If your dog is worried, this is the shape of the work
Gradual departure practice, kept below the point where your dog starts to worry, is the core of separation-related behaviour work. Staying under that threshold is the condition for learning. It is slow on purpose, and it is where a qualified behaviour professional earns their fee.
The rule underneath it is that your dog is not left alone for longer than they can currently manage, at any point during the work. That usually means arranging cover, which is inconvenient and is still the fastest route.
Safety note
Book a veterinary examination first if your dog cannot be left alone. Distress at being left is a recognised behavioural condition. Sudden behaviour change warrants a veterinary check, and pain often presents as a change in behaviour. Then ask your veterinarian to refer you to a qualified behaviour professional.
Three things not to do
Do not get a second dog to solve it. A dog worried about your absence is usually not comforted by a different dog.
Do not leave your dog alone for longer to prove they can cope. That rehearses the panic and makes the next departure harder.
Do not reach for a bark collar. Punishing distress adds fear to it, and aversive methods are associated with worse welfare outcomes and no training advantage.
How long this takes
Boredom often shifts inside 2 weeks once dinner comes out of a bowl and into a toy tied to your leaving. Genuine distress is measured in months, with help, and nobody can give you the end date.
Tonight's version, in one line: film 10 minutes, then decide which of the two problems you actually have.