It really gets me fuming to hear about stuff like this going on, as it's exactly the kind of thing that will stop some people from ever fishing the park.
The coppers really need to get off their arses with this, it's no good them claiming they never hear about anything going on, if they took the time to send a even a couple of patrols around the park on a regular basis they'd soon find out about the crap that goes on in Leazes from time to time. Anyone with an ounce of sense should be able to realise that, unregulated a city centre park is gonna be a magnet for trouble.
Fishing should be about relaxing and enjoying yourself, not constantly watching your back for random attacks.
As to taking things into your own hands, me and my mate work on the principle "Always keep a bankstick handy", if we ever were forced to defend ourselves though I don't reckon the plod would see the funny side of a charva with 2 foot of aluminium tubing stuck up his jacksie!
Sorry to hear about your misfortune mate, but don't let it keep you from fishing.