i heard that some snow kniters 'Doubble up' with a extra pair of lines attached on their main flying lines,
this can act as a back up, under heavy tention the lines could snap,
so having a second pair of lines is a good safety measure.

does anyone know if this is true? if so, how would you keep them together?

This is possible although i'm not sure of anyone doing this. Its important for safety to no less then check your lines and make sure you have a backup for sure. The only thing I can see maybe a problem with doubling up is this most kites have leaderlines or a series of ropes that come from the bar and attach to the actual kitelines. I don't think it would be possible to double up on these cause they are waaaay thicker then the flying lines. I just read on another forum of a guy that had an issue of the bar wearing at the attachment points on the bar and a leader snapped dropping him nearly 30feet. The other thing is most of the "Kiteboarding lines" are nearly 800 pound test spectre times 4 that is nearly 2400 pounds of security. even under high g's they should never become a problem. Although they need to be inspected either every ride or definitely if its a epic condition day and you wanna go bigger. Any knicks from edges, snags, or anything else that could compromise the integrity of the lines should not be overlooked.

The whole double up idea comes from gliding. If you plan on gliding down hills then you should take extra care in your lines, either double up, get the q-line pro and make the larks' knots. Or always use brand new lines. I've had lines break on me in the water, and if that we're to happen 30-50ft in the air,...well you can imagine. Under heavy stress lines can break, they eventually stretch and lose some of there strenght. Its easy to add an extra line, just slide down the larks head knot as it is attached, and attach another one. This will add to your line drag, however. Which means a lil less response between bar/kite. Might even slow the kite down.

Another thing, most kite companies use cheap material to keep overhead costs down. are you going to let your life hang from a kite that is "made in china" and not up to the specifications that paragliding wings are REQUIRED to pass. Ozone kites are so far the only one to really address this issue. (there a paragliding company as well) Most kites aren't designed for this kind of flying, its quite a bit of load.

Just something to think about, i like gliding and think it one of the funnest things to do on the slopes, but i still think its dangerously stupid.(maybe thats what makes it fun?)

just my 2 cents,
Sol