The whole vandal / liability thing is getting way out of hand. Our obsession with making everything completely indestructible is an over-reaction to the problem. In the case of making dry stone walls less vulnerable to senseless damage, or the possibility of people hurting themselves on them, we are missing the point if we have to bring concrete into the equation. The answer is not to taunt would-be vandals by challenging them to find new ways to destroy the bunker-like objects we introduce to our parks and public places, but to consider natural designs that are much more effective. In the case of liability concerns, what was God thinking anyway when he created trees and stones. How could he have been so careless as to create steep hills or ponds? In the case of vandalism what was he thinking when he made just about everything? We need to ask ourselves whether creating things that are more 'natural' and hence more vulnerable to mischief, might be more effective in maintaining damage control.
A dry stone wall works not just because it is strong and structural but also because it 'yields' to the forces of nature rather than obstinately resists them. The whole idea of yielding is the key to the problem of public installations. In the same way dry stone walls 'yield' to the vandalism of the elements, they can also assimilate many of destructive elements of society.
A vandal will be less likely to try to wreck something that is not challenging his imagination as to how to take it apart. He is also less likely to carry away or destroy the stones that he does manage to take off a wall. The whole idea is to accept the fact that nothing can be made vandal proof but that things can be designed which involve materials that can be taken apart but not actually broken or built in such a way that they can be repaired easily and quickly. We can introduce less confrontational elements into the community by tuning in to how to care for our walls, which on occasion may suffer from abuse, rather than designing war zone installations that are more abusive to our sensibilities than anything a vandal could do.