Presumably Yasgurs Farm was the site where the Woodstock Music Festival took plce 40 years ago.(Has it been that long?) I can't work out the entire anagram yet but the ARM part of it must be "a jolly" i.e. A Royal Marine.
Looked up Yasgurs farm and Woodstock took place there. I think you are right about the ARM which leaves SF to complete anagram Science Fiction perhaps ?