Keep a log of every time he does this. Also log every time you call police/council and include dates of all this when you next call.

It's a good idea to send complaints by email too as there is a paper trail.

When you call the police/council log the time of the call and the name of the person you speak to and mention this in future calls, "I spoke to Josh 4 days ago and he advised....”

I believe the council still provides a noise meter to record loud prolonged noises.

Any time he is in your garden brandishing anything then call the police and advise them that he is on your property with a weapon.