It seems your talking yourself out of ferreting this area, most will give you the same answer, cut the brambles down a few weeks prior, or ferret it as is, and keep fingers crossed that you dont get any digs, lots will stick up pictures of nice flat ferreting areas, but Im sure most of us, still have patches as bad, if not worst than your saying, its what ferreting is all about, you'll need a longnet to encircle the brambles, otherwise you'll miss pursenetting lots of holes within the brambles, then get a decent shovel, and dont forget the locator