Well the truth is mine are very capable of going over the boxes when they are willing to and they are meeegggaa strong ( they can knock over a heavy big wooden box with other piggies inside) but they usually Don’t want to go outside as they don’t like the hard floor and they feel scared in such an open space. At night we put them into their cages anyway (1meter x 1,5 meters) so I have no fear that they might escape. Once we had a cupboard there and the pigs kept making their way through to under the cupboard, however hard I tried to prevent them.