North African close to climbing secure borders (6)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

reversal of (climbing) NAIL (secure) around (borders) BY (close to) Another one where the wordplay did fool me. I felt sure we were going to have a ‘G’ in a word meaning ‘secure’. I know the African continent fairly well, and know which countries have the right number of letters and which are in the north, but even after getting LIBYAN from the crossers, I had trouble seeing how the wordplay worked.