Ping a body hair folicle drug test?

I have a friend whom has been clean for about 3 and a half months... he's failed one body hair follicle test which dates back 12 months but has ped all random U/A tests and has acquired custody of his kid over the mother whom has failed and refused testing. His concerne is that in 6 months he is scheduled to take another body hair follicle test in which if he should p the mother cannot dispute custody. I advised him to shave all of his hair off and in 2 weeks shave it off again... and then re grow it. His fear is even though by that point he will have been clean 9 months... will there still be trace amounts that show up? By Shaving and re-growing his body hair without the use of illicit drugs... can he pass a body hair follicle test which is supposed date back 12 months even though he has only been clean 9 months by shaving and then re growing??? If there are any experts or persons with first hand knowledge who will please assist me with correct answer that will assist my friend... in securing the custody of his child without having to pay dearly for his stupid mistakes.