I would steer clear of natives (bottle brush) as they have a tendancy to die suddenly after a number of years. The pittosporum suggestion would work. Marayas (mock orange) would be a really great choice. They are quick growing, bushy and thick but not strong enough for someone to climb on. They get beautifully scented blossoms after rain all year round and little orange berries which aren't harmful. Also only need a prune once a year or so to maintain shape if you want.