Hi: I am having a 7high stockade fence put up to replace an old one. I am using all pressure treated wood with 4x4 posts. My question is - do I need to put 4 rows of 2x4s across each section to screw the boards to or can I get by with just 3 rows of 2x4s? Most fences ive seen have 3. The fence is 380 around the yard so the extra 2x4 would be another added expense that im not sure I need. We will be using screws instead of nails. Thanks for any input....