John McMillan wrote:
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.

Vicious! I hate more the taste than what nature has given them. 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?