If Castii Canubi is a magisterial teaching, (which I believe it to be) then NFP is something a Catholic cannot/should not implement.
Now if Castii Canubi is NOT a magisterial teaching, I would still say NFP is something a Catholic cannot/should not implement.
With this very serious issue, I will bank on the option that forces me to cultivate virtue. I truly believe it's as simple as that. I am not smart as you guys with the theology, I'm simply just not, so I will yield to what the Church fathers and natural law taught/teaches.