Phil, I have the setup such that there is no spare halyard when the kite is down. I've also put a shockcord loaded block under the tramp coming from the back beam which hopefully will pick up most, if not all of the slack when the spi is up. the halyard is under a lot of tension when the spi is up so there isn't any chance it can go astray then, only maybe during dowsing. mmmm If it can it will.
I guess a small string linking the 'Leslie' spreader arms wouldn't be such a huge impost.