In June 2009 we fenced around a nursery in Stanningley, Leeds. These are simple picket fences with matching gates made using 75mm wide tanatone (brown pressure treated) pales. The gap here is 50mm which is narrow enough for security but wide enough to allow enough light through to stop it being to shady inside. We always use exterior decking grade screws, and not nails, which means that the pales can’t easily be kicked off.