Your dog is 11 months old. A guest sits down, or the children come in from school, and your dog is on a leg. Ten minutes later they are working on a cushion. It is embarrassing in a way few adolescent behaviours are, and it is badly misread.
What this usually is
In most adolescent dogs, humping indoors is arousal with nowhere to go. It appears at the peak of something rather than out of a calm room. It shows up in dogs of every sex, neutered or not.
The other common driver is stress. A dog who is unsure what to do with a stranger in the house, or with too much happening at once, sometimes lands on this.
The status story you will be told does not hold up, and it points you at confrontation. Punishment-based approaches are associated with fear, avoidance and defensive aggression, so that route costs you twice. Reward-based methods are what the veterinary behaviour guidance recommends instead.
Learn the 10 seconds before
There is nearly always a run-up. Panting with a wide mouth, pacing, whining, a fast circling approach, or paws going up on somebody. That is the moment to act, not the mount itself.
Interrupt, then redirect
Stand up and step away without a word. Standing removes the leg, and silence keeps you from adding volume to a dog who has too much already.
Hand over a different job at once. A chew on a mat, a lick mat, or 10 pieces of food scattered on the floor.
Sniffing and chewing are the fastest routes down that most dogs have. Neither one needs your dog to be calm first.
If nothing lands, put your dog behind a gate with a chew for 3 minutes. Dull and brief, not a telling off, and back in when the room is quieter.
Pick the cushions up for 2 weeks. Removing the rehearsal is faster than interrupting it 40 more times.
When guests are the target
Have your dog on a leash or behind a gate before the door opens, with something to chew. Arrivals are the highest point of the whole visit.
Let the greeting happen 10 minutes in, once your guest is sitting and the excitement has come off. Keep it to a few seconds, then call your dog away and pay them.
Brief your guest in one sentence: stand up, turn away, say nothing. Ask them not to push your dog down or laugh, because both are attention.
Set your dog's station up 8 feet from where people sit, and pay them for lying on it. A dog with an address in the room has less need to invent a job.
The thing underneath it
This behaviour clusters in dogs who are short of rest. Relaxation is trained as a behaviour in its own right, in short repeatable sets below the point where your dog gets restless. Around the onset of adolescence, dogs also respond less to the cues of the person who raised them. That is why calling your dog off mid-mount rarely works, and why removing and redirecting does.
Safety note
See your veterinary practice if the humping is frequent when nothing is going on. The same applies if it comes with licking at the area, straining, or a change in toileting. Sudden behaviour change warrants a veterinary examination. Get help now if your dog growls, stiffens or snaps when interrupted, or if a child is the target. That means a veterinarian and a qualified behaviour professional.
Today's version, in one line: put the cushions away tonight, and have a chew ready by the door before your next guest arrives.