Use the Ball & Chain to destroy the lookout tower next to the fence, transform into a wolf, and walk through the gap. Then on the second fence, go over to the right side (GCN) and just try and wedge your way through it.
After trigger the Bulblin archer cutscene, run over to the left (GCN) side of the barricade and wait for a little while until one of the boars runs into the wall, launching the Bulblin riders onto the wall. As a wolf, get near to the wall and use an area attack to target the riders. Walk back a few feet from the wall and use the area attack to super jump onto the wall.
The trigger that loads the path to Arbiture's Grounds doesn't exist until you defeat King Bulblin and break through the fences with a boar.
When you enter the Bulblin Camp, immediately perform the Map Glitch and backwalk off the solid ground. Do a jumpslash while falling to give yourself forward momentum. If done right, you will clip into the cutscene trigger, which will reposition you above ground.