I am having enough trouble managing my own 1/4 acre, but I love the idea of urban guerrilla gardening. Richard Reynolds, who wrote the book On Guerrilla Gardening, says it is "the cultivation of someone else's land without permission." In the 70's Green Guerillas cultivated empty lots in Manhattan's Lower East Side by jumping or cutting fences or throwing "seed bombs" (Christmas ornaments filled with seeds and fertilizer) over them.
These days some guerrilla gardeners grow food, some take over private land as political protest, and others, like Reynolds, just want things to be prettier. Were I to be a guerrilla gardener I would have a hard time deciding if I was the first kind I mentioned, or the last.