Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Scottie, watch their toilet habits and their energy. Peeing more often, straining or blood in the urine can be the first sign of bladder cancer, and it is easy to mistake for marking. A Scottie who is heavier, slower and grumpier than they used to be may have an underactive thyroid rather than a bad mood. Gums that bleed, or a cut that will not stop, are worth telling your vet about. Bloat (GDV, a twisted stomach) can happen in any dog, though it is most common in large, deep-chested breeds. A swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling is an emergency: contact your vet now.
They'll come for a fuss when they're ready. If they stop wanting one at all, tell your vet.