Justplainpossum, is there not some sort of waiver you could have someone sign relieving you of any liability if they came on your place and hunted the hogs. There are plenty of people that would be happy to take care of the problem for you.
To answer your question, I would go with a semi auto, something like an AR in 6.8 SPC would be ideal though maybe hard to find right now, perhaps a Browning BAR in .243 or something similar.
http://www.browning.com/products/cat...id=031&tid=330