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 Min Pin, watch their back legs and their stamina. A young dog who skips, lifts a back leg or chews at a hip may have a kneecap or hip problem, and they will keep running on it. A dog who tires sooner, coughs or breathes fast at rest may have a heart problem rather than a lazy day. In an older Min Pin, a slower, heavier dog may have an underactive thyroid. 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 keep finding the gaps. If they stop looking for them, tell your vet.