If you're an eye for an eye kinda guy like me, and willing to spend a few hours googling what I'm about to tell you, since I'm just giving the basics here, you'd want to give him some of his own medicine.
You will need:
1. 1 x old but still working microwave oven
2. 1 x set of tools including a screw driver
3. 1 x waveguide (basically a dish - google will tell you what you need)
Process:
1. Take the oven apart and re-assemble outside the enclosure
2. Locate the magnetron tube (which broadcasts microwaves at around 2 Ghz) and mount in centre of waveguide
3. Again leave a note at neighbour's door stating that his fence is messing up your tv signal
4. Wait til dark
5. Point magnetron/antenna at neighbour's TV antenna / dish
6. Stand well clear. As in make sure there is a wall between you and any other living thing within 30 metres and the tube. Unless you want your corneas to turn from clear to white like an egg that's cooking
7. Switch on and run your modified oven for around 5 minutes. You might hear your neighbour swear at SABC/Mnet/DSTV during this time
8. Wait an hour
9. Repeat process until he gets fence repairmen out
For maximum effect, schedule your "cooking" at the same time as the Springbok / NZ or Kaizer Chiefs / Pirates game, as applicable.
Ok, just joking! (It will work, but you might want to put your lawyer's number on speed dial, since it may not be very legal

).
Your best bet is to get Icasa / Sentech involved. They don't like anyone broadcasting on their frequencies, even if it is only a fence.
Best of luck!!