Originally posted by Let's Go Brandon:

BUILD A PIT!


Problem solved

I think GunsForBucks' experience could successfully refute that this always solves the problem and that's supported by Cockpuncher's linked discussion. I've had half a herd of boars poof away from a base surrounded with moat & terrain wall with no solid AI pathing out of it. Plus they were in a livestock-fenced pig pen.

From the various comments I've seen it is certain some folks' pig enclosures need work but others appear to be experiencing something buggy. I suggest that people keep some excess boars around to use as back ups :-)