My dog won’t stop barking at people as they walk past the gate. How do I stop him?

Firstly, do not allow him access to the gate. “Garden gate” dogs bark at passers by for different reasons. Some might find passers by threatening or a bit scary or even a fun game. They bark and the person carries on walking past so the dog achieves its
goal as the man has gone and the dog feels good so is more likely to do it
again the next time. This whole process is self-reinforcing and no amount of
shouting, “be quiet” will suffice. In fact if you shout too much all you end up
doing is proving to your dog that passers by need to be sent packing as every
time one appears you start shouting. Instead introduce lots of fun training games and extra walks as Collies are high-energy dogs. Get them working for you so they don’t go
self-employed and enjoy more time doing things together.