I'm gonna make a quick visual guide on how to it in
1. the wall
nice wall eh
2. the ZOOM
zoom like, a lot to a corner or the top part of the fence. since you don't want the fence to look like a long rectangle but a fence. (you'll see what I mean)
3. Extrusion tool
hgsssssssss *chinese face*
the zoom from earlier was to allow us make the lightest extrusion possible
one for the fence and another one completely transparent (latest SM64 OBJ Importer allows for Alpha importing, so you can safely use the sketchup opacity slider.)
5. textures (positioning)
to do same with the second face use the eyedropper tool (alt+click with the material tool, will copy the texture properties) then texture the other side.
now you see the little borders from the extrusion we just made
use the totally transparent texture on these
6. OBJ Importer (SM64 Editor 2.0.x)
let both textures be default.
that's what works for me, if someone else has another solution different from what I said please tell me