In article ,
K wrote:

John McMillan writes

No-one has mentioned gooseberries which have vicious thorns.

Actually, for maximum deterrence the plants not only need thorns
but should be clearly seen to have them.

My favourites are Rubus Cockburnianus (ghost bramble)
http://davesgarden.com/pf/showimage/4179.html/
and Rosa Omiensis Pteracantha (r.sericea pteracantha)
http://www.rosesloubert.com/collecti...20omeiensis%20
pteracantha.jpg
which has very scary looking blood red thorns.

They're scary looking but they're kittens compared with gooseberry,
pyracantha and even hawthorn


I think that was my point. Its largely psychological deterrence
you want so scary looking is better. Having said that, its probably
worth growing a mixture of these things.

Vicious! I hate more the taste than what nature has given them.
Never mind. One of my favourite fruits actually.

But
it's not going to help the Serene. It's the access to a roof if I
remember it right. Gooseberries are quite low, aren't they?

They normally start life as 30cm shrubs but can grow to 1.5m bushes
in a few years, depending on type. They're not climbers certainly.
Planting them at the bottom of drainpipes or other structures you don't
want people to access is a good move.
They take quite a lot of shade, don't seem to
mind poor soil. And if you don't want to eat the fruit, the birds will.
A huge visual improvement on razor wire, broken glass, spike topped walls
etc etc.