Maybe you can make a charitable donation to the school in the way of landscaping plants for the grounds and maintenance crew. Our
local Lowe's was clearing out their ornamental kales for a dollar a pot, so I picked up a few. Since these look like landscaping and not food, you can do your guerrilla
gardening without any subterfuge at all. Just some plants to spruce up the walkways and planter boxes on campus. Then after they go home for the evening, you can return with your pruning scissors and do a little
harvesting upkeep.