I was thinking of pyracantha, I've already planted some to stop them
climbing over a low fence and its vicious stuff :-) I guess, apart from
being spiky, the main attraction of a hedge is that its self-repairing.

I don't know if it applies to private property, but we have been warned that
if we plant a 'barrier' hedge such as spiky things, we could be prosecuted
if anyone gets damaged or their clothes are torn etc etc in this PC
world:-(( . This is in connection with a public path of over 130 metres
long bounding a piece of land owned by the Parish Council.

Might be worth checking.

Mike