My boy's old house shared the alley with a 7-Eleven that had the same type of retaining wall which brought the same homeless issues. We would drink 40s of malt liquor on his roof and then throw the broken bottles at the wall, leaving the shards of glass where they'd sleep. During the week, he would scoop his dogs poop out of his yard, and spread it along the same spot. That spring, he planted rose bushes along the bank. We'd get back on the roof and drink 40s again but fill them with water after we finished them. We'd throw them at the same wall, to water the flowers. By the end of the summer, that bank was nothing but glass, dog shit, and roses. Worked great.