Have you ever watched "Survivorman"? He outlines a couple of neat little tricks that could be employed here... like a snare that would at the very least hold the cows in place until animal control or the sheriff could come and remove them, another is his fish trap... and I like this one best for your situation... put a post on each side of each of the holes in his fence, then put sharpened sticks on those poles with the sharp end facing the center of your property in kind of a V shape. The cows will walk through to your property, but will not go back, so in about a week, you can rent a big tractor trailer and haul them all off to the auction... just remember to do something nice with some of the money and buy him a few hundred feet of barbed wire. Buy a nice new truck with the rest. :evil:
Or you could maybe file a lawsuit against him for the grazing value of your property multiplied out over the past few years, with interest and punitive damages for not paying you up front, then offer to settle the suit with him for the price of fixing the fence plus your filing fees.