I'd like to know myself as someone here has started it. I keep watching but can't figure out the culprit. I want a piggy cam as would love to see who does it and see if can work out why. Whoever it is did a real job on Teasle, Tia and Tansy all over in a couple of nights. Most of their coats seem to be growing back now but the fringes are staying short so makes me think someone is still at it. Generally it doesn't bother me as not harming anyone but sometimes could weep to see their flowing locks.
I think I read before there was something harmless but bitter tasting you could dab on their coats to stop it but can't remember where I read that or what the substance was.
EDIT to add - forgot to say I did read an article not long ago by someone who had perus and after a new addition to the group barbering started. This person worked through various things like more hay, more pellets, more toys etc and eventually after about 4 weeks the long hair started to grow back but wasn't sure which method had worked or if the barber just stopped of own free will.