It struck me that it might be useful to place the responsibility on the fathers shoulders in the following way.

Each time an incident occurs, write a letter to the father explaining what has happened - something like "I'm sorry to have to inform you that your son threw a bottle at me today ..." etc

Each time you do this, you keep a copy of the letter.

Each time you do this you inform the police and inform them that you have written to the father so HE is aware what is going on.

You ignore the idea that "the police can't do anything".

The police will do something in the end if you continue to report what is going on.

When you report to the police, you write a letter and keep a copy.

Cumulative pressure on the police will force them to rake responsibility in the end, especially if you start complaining and making an embarassing but very civil and patient fuss.

That means making a fuss and not giving in - ever - but always being civil so they cannot complain.

Don't give up!!!

Do everything by the written medium and keep copies of everything.

At some point you will be able to complain to the police as your pile of letters gets higher and they and the father will have to start wising up.

Find out about thhe policies and procedures that govern police responsibilities and you will find aa way to force the police to help you.

That IS what they are there for and the father is responsible for the actions of the child.

Be informed - be proactive!