Erecting wooden barrier posts - give support to please? Can any tell me the correct diameter to verbs the holes for...

Can any tell me the correct diameter to verbs the holes for fence posts? - The run of barrier will be 40 feet long using 6ft X 6ft panel - my concern is that the location of the fence usually get hit quite concrete when it is windy and I entail it to be stable.
Any help treatment.
Answers:    Go for 8feet 3x3 post with 2 foot in the ground. 4x4 are to robust for panels and look strange. Make sure posts are concreted in.
the diameter shouldn't manufacture any difference just craft sure the posts are in nice and vast, use post holders as well for more stablilty