Step 2
Using the kite end pull a loop through the first loop.
This a quick release knot I found in The Handbook of Knots by Des Pawson.
It was called a Highwaymans Hitch which I suppose translates into Cowboys Hitch if you are American.

I have never had it fail (a sign of failure is the final loop shortening). However, if the kite is on the ground and someone pulls on the spool end the knot releases. Hence the safety measure of putting something through the loop.
Quick Release Knot (Highwaymans Hitch)
Step 1
Pull a loop behind the tie off item (webbing, peg, post, fence wire).

Step 3
Using the spool end pull a loop through the second loop. make this loop at least 10cm long.
Step 5
For larger kites place a carabiner through the final loop. I usually leave the carabiner on the webbing.
Step 4
Hold final loop and pull on the kite line to tighten the knot.
To release the knot:-
1. Remove the carabiner or what ever you put through the loop.
2. Take the tension off the kite line.
3. Pull on the spool end of the line to undo the knot.