I like the rock idea.
People get territorial even about places they don't own. Eventually, you will win by creating something new & beautiful in the space they previously assumed was theirs to walk through. When I was first growing trees on my property, which was barren and frequently crossed by pedestrians/kids/dogs, I withstood anti-plant assaults for years. A neighbor "helpfully" came along to top my new tree. Next, a driver felled it, then wrote me a check to replace it. Another neighbor used to take pictures of my yard & send to the city till I saw her doing it and confronted her.
I knew I had finally won when one day I was trimming my bushes and a woman asked me not to cut them back too far because it made the neighborhood more lush.
Anyway, years later, the yard is widely admired.
Strategies:
Use very large potted plants/flowers as a border. Bamboo in a pot is very fast-growing. Never put it in the ground, however!
Put up a sign about the amount of oxygen created by the trees & plants, and birds/pollinators attracted to the organic flowers.
Use sculpture, artwork, fountains, decorations, etc. to get people realizing that this is a garden, not an empty lot.
Create a dog-poop-bag station/water bowl with a sign pointing to dispose of bags in the trash.