I've been thinking about the staring problem some.
I guess the first question would be is the staring a genuine threat? The next question would be if confronted, would it become one?
If no to question one then ignore them, but I remember not being able to do this at school when told to! If you believe said individual will become nasty if confronted then leave well alone too. Most people would be embarrassed while confronted however, as they wouldn't expect to be. Maybe give them an opt out so it's an irimi not a clash, e.g.:
"I've noticed you looking at my garden/curtains, you must really like them."
Legally staring at someone continually, may well constitute harassment, so this could even be an option (ask hubbie I guess).
Put up mirrors so they can see how silly they look.
Get some ugly friends to make out in view...
Get a life size cardboard Steven Seagal to stare back!