I agree, even lead isn't long term, except to the ones you kill of course, but it's the most effective.  Repellents do nothing to reduce the population and so far I haven't heard of any that deer don't grow accustomed to.  Using repellents to funnel them to places you can kill them can work but population reduction is the only long term answer, even though it means doing it every year.  I can't imagine what our population would be like without our depredation efforts over the last 30-35 years.  Thermal scopes on a suppressed rifle are the ticket to saving this year's crop but you'll have to use it to save next year's as well.