You will need to have a word with the police in your area - using material whch can be potentially harmful to anyone climbing over your barrier may leave you open to a legal case against you. I realise the apparent injustice of such a system, but the law is the law, and we are all bound by it. While you're asking for advice on the height and construction restrictions of your barrier, why not ask the police to send a few more patrols round, and see if they can eliminate your problem that way.