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 Border Collie, watch their focus and their nerves. A collie who suddenly starts chasing shadows or lights, or who is newly frightened of noise, is a reason to contact your vet, because both can have a medical cause. So is a limp after play, a dog who stops wanting to jump into the car, or any seizure, however short. A first seizure, one that lasts more than two minutes, or more than one in a day is an emergency: contact your vet now. So is bloat (GDV, a twisted stomach): a swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling. It can happen in any dog, though it is most common in large, deep-chested breeds. In an older collie, restlessness at night or forgetting a routine they knew can be the start of cognitive decline.
They'll keep watching your feet. If they stop caring about your shoes, call your vet.