I've been sliding since 1969, in standard tuning or dropped D -- I tried but abandoned open tunings -- and I've developed a 'behind the slide' technique ( example at http://www.thatllteachyou.com/glix ).

If anyone's interested in more lessons on the subject, there are a few loaded up at http://www.thatllteachyou.com/granted.html

Anyone care to discuss slide technique?

Kirk