Sanm it is indeed in Chelek 1 – in Siman 37. The teshuva can be read on-line at http://www.hebrewbooks.org/pdfpager.aspx?req=20021&st=&pgnum=119 (at the bottom of the page).
In any case, everyone agrees that it is prohibited. The only question is is it because of lo tikravu and yehareg uval yaavor or derabbanan because of a fence and devarim mechuarim, in which case it is not yehareg uval yaavor.