David Carter in the UK,
I don't know what possessed Mr. Corbin, of New Hampshire's Corbin Park to do it,
but he did exactly that when he stocked it with all sorts of animals:
"214 Prussian wild boar from the Black Forest of Germany,"
according to the (online) accounts from 1956
when somebody sued the game preserve.

When Mr. Corbin had the preserve constructed, it is said,
the fencing went down three feet into the ground,
with the boars/hogs in mind.
So, if the hogs took a notion to tunnel out of the game preserve,
they had to dig deeper than three feet in order to do it.

Mr. Corbin and his succcessors in New Hampshire
reckoned without Mother Nature however.
On two occasions the fence was no impediment to the hogs:
one, during the infamous hurricane of 1938
(rare for New England to get hit with a full-force hurricane,
and that one made history),
and two, forest fires that took the fencing down.

Thus, there are escaped hogs near the Connecticut River in New Hampshire,
and some are said to have swum the river to the state of Vermont.