(no fences) - with adequate warnings; cheap and effective...
Well, of course warning signs would be mandatory.
The fences are needed too - for really stupid people and those who never learned to READ.
Trump’s executive order challenging birthright citizenship faces first legal test in Seattle court:
Yes and a fence a good place to hang a sign, mainly because wild animals will wander into a mine field so best with a fence or two. Also frozen ground can activate a mine. As I said, the 'Iron Curtain' hardly needed signs or warnings - any sentient being knew where not to walk.