I would suggest that you book some one to one training with a trainer who specialises in border collies before this problem gets totally out of hand. Sorry I can't suggest anyone in particular as I don't know where in Scotland you are but your vet will most probably know the most experienced person in your area. Alternatively, Google for BC kennels as many of them supply trained or part-trained dogs and will do one to one training where there is a problem.

Sgurr