A good high tensil net and a really good 4 point wire right on the ground. You don't need a real high net. 39" and 42" should be available locally.
What you must have.
High tensil
A one piece vertical stay
A fixed knot.
A good tight spaced sharp barbwire right on the ground. This makes a big difference. Pigs go under, but they lead with their nose and barbwire does deter this. Tornado makes a good wire with a four inch space and staytuff makes a predator control barbwire with a 31/2 inch space. Last things gotta be tight. Not pretty tight, or good enough, I mean badazz tight.
If you had good braces and a good existing fence infrastructure where we could stretch right on top of the existing fence. You would be looking at 2.00 a foot material and labor.