There are a number of low retaining walls outside my office. They are the type designed to contain flower beds or some nice shrubs. In our case they hold back a few rusty old street lights (which some workers were 'felling' the other day) and some bare earth.
In Port Moresby there are always a lot of people hanging about, as a lot of them have nothing else to do and hanging about fills in the time. One former favourite spot for hanging about aimlessly was outside our office on these conveniently seat-height retaining walls. Of course there are notices saying don't hang about, or sell things or generally be here, but these are duly and completely ignored.
A few weeks back the security guards hit on a good way of improving compliance with the no loitering instructions. They got some old sump oil out of the generator (or someone's car) and poured it liberally all over the prospective seats. Problem solved. No one sits there any more and all it takes to maintain is an occasional dousing with old oil.
It looks so attractive too, don't you think?