I cast off/bind off/tie off my flat panels like the regular casting off - (round ) Tips: Make sure that the tail string is where you will END! Regular casting off - there are some great vids on you tube- just google casting off flat panel -
There is also the "draw a thread throu all the loops, and crochet it closed, and there is another binding I have found called stretchy bind off - (because regular casting off leaves it a bit - :tighter with no stretch -: - (works best on circle things,)
Here is a regular cast off -_and a panel, too! (with pick tool)
easy! (mikeyssmail vids are great!
http://www.youtube.com/watch?v=c-9WEN3QJAI
Here is another method: Fayme is doing a blanket cast off (another way - on round loom (panel) http://www.youtube.com/watch?v=cCY-Zq62G_E&feature=related
Here is a crochet (flat panel vid - you have to watch a little to see her end -) http://www.youtube.com/watch?v=BlVu9yAw3Ko&feature=more_related