Algeria is actual the only map (for ntw and etw) which has those fences, so they are the only possibility to research this issue.. thats why i refer to them, as "algeria walls".What do you mean with Algeria map walls?
None of both.Primergy, which file you copy to the custom map? buildings list or the props list?
Fences, Walls and field props (if used in a farm_template) are placed via the farms.farm_manager file. Actually it's a bit complicated to get hands on this file of the algeria map and only possible with Taw's Tools (A big thank you taw!).
You also have edit a bit of his code to get the file extracted.
If you want i could send you a xml file of the farm_manager and a already converted version, so you can try around yourself (as long as ntw still uses the same technqiue).