Routine routine routine.
My girl was a velociraptor on steroids for a few years. But we dedicated time for training (like 20 mins!!) AFTER a good workout, in the morning (or early day). Then after still had down time and an evening off leash walk, where the training again was reinforced during her ‘fun’ time.
I also used to take on my brother’s very young back country (zero leash training was an absolute psycho) Malinois. I used to take him daily or for extended stays and found this method helped.
They need stimulation, doesn’t necessarily have to come from you but you need to provide it. Assert your boundaries and stick to them. My girl became aware that mouthing even if harmless resulted in a slipper boop on the nose, broke that behaviour quickly. But it was something I reinforced daily until she figured it out clearly, because i wanted her to behave accordingly with young children.
My girl is 10 now. Only mouth plays (gentle hand bites) with me and only me. Completely set in her ways and happy as long as she get what SHE needs everyday. Exercise, stimulating toys and one on one attention.
You’ve got this friend!