Action needed to keep park clean

What I cannot understand is that people can live in the park, have access to free water, strip the park of whatever is needed plus bark from trees for their fires, seem incapable of cleaning up, urinate and defecate everywhere except the toilets.

Yet it seems there is absolutely nothing local residents can do about it.

Surely if nothing concrete is done, it will encourage more and more vagrants into the park until it is overrun and is no longer a facility for law-abiding citizens.