How can I hang my garden art without nailing or drilling into walls?

Unfortunately, there isn't an easy answer to this question.  First, temporary adhesives don't usually work well outdoors and permanent adhesives will leave residue or damage the stucco.  Top hangers may be your best option, but they may encroach onto your neighbors side of the fence.  If that isn't an option, (assuming it is a block wall underneath the stucco) then you could try using screws and molleys drilling a pilot hole first.  You'll just have to use some caulk and touch up paint when they are removed.