Had this been me, at some point I'd have driven to the bar, and asked the biggest guys I could find if they'd take $500 to show up at the guy's house and scare the living crap out of him. Escalate accordingly. There aren't that many situations left in this country that call for intimidation / violence, but malicious litigation is one of them.
I agree under 2nd Amendment authority. All others have to be exhausted, though, before that can apply. So, first try your Congress people about passing laws limiting it. See if the LEO's will do anything about the abuse. Try the courts. If they all ignore the corrupt behavior, you're left with no choice but using violence to deter the aggressor. Just make it untraceable with an alibi.
What makes violence a viable option is the fact that you're dealing with one person and not an organization. If it's more than one person's efforts you have to counter, then yielding is the better recourse. A group of people will have a goal in mind when taking action against you, all you have to do is help them reach that goal and they'll bugger off. You can fight a group effectively but it's generally not worth it.