[gladis]

how much feathers do i cut off to stop them flying over 6ft fence

[joyfull]

here is a diagram:-
http://www.poultryhelp.com/wingclipping.html

remember to only clip one wing then after they moult if you want to clip again clip the opposite wing.
Some birds can still fly quite well even with a wing clip.
I don't bother clipping as I like my chickens to be able to fly out of harms way.